X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=src%2Fdatastore%2Fdatastore_api.c;h=ff49c106e5a944c5548d9b7753e1c67ed574e9b6;hb=5746309cb4be2073d550ad7a6885e918631dbc38;hp=73783cfb8bdc744e7ee4b2fbb68eb39a1a2cf187;hpb=7bc466bbdb8b64cac68c5ee59eb7ab6b9d85c420;p=oweals%2Fgnunet.git

diff --git a/src/datastore/datastore_api.c b/src/datastore/datastore_api.c
index 73783cfb8..ff49c106e 100644
--- a/src/datastore/datastore_api.c
+++ b/src/datastore/datastore_api.c
@@ -1,10 +1,10 @@
 /*
      This file is part of GNUnet
-     (C) 2004, 2005, 2006, 2007, 2009 Christian Grothoff (and other contributing authors)
+     (C) 2004, 2005, 2006, 2007, 2009, 2010, 2011 Christian Grothoff (and other contributing authors)
 
      GNUnet is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
-     by the Free Software Foundation; either version 2, or (at your
+     by the Free Software Foundation; either version 3, or (at your
      option) any later version.
 
      GNUnet is distributed in the hope that it will be useful, but
@@ -20,16 +20,158 @@
 
 /**
  * @file datastore/datastore_api.c
- * @brief Management for the datastore for files stored on a GNUnet node
+ * @brief Management for the datastore for files stored on a GNUnet node.  Implements
+ *        a priority queue for requests (with timeouts).
  * @author Christian Grothoff
  */
 #include "platform.h"
+#include "gnunet_arm_service.h"
+#include "gnunet_constants.h"
 #include "gnunet_datastore_service.h"
+#include "gnunet_statistics_service.h"
 #include "datastore.h"
 
 /**
- * Handle to the datastore service.  Followed
- * by 65536 bytes used for storing messages.
+ * If a client stopped asking for more results, how many more do
+ * we receive from the DB before killing the connection?  Trade-off
+ * between re-doing TCP handshakes and (needlessly) receiving 
+ * useless results.
+ */
+#define MAX_EXCESS_RESULTS 8
+
+/**
+ * Context for processing status messages.
+ */
+struct StatusContext
+{
+  /**
+   * Continuation to call with the status.
+   */
+  GNUNET_DATASTORE_ContinuationWithStatus cont;
+
+  /**
+   * Closure for cont.
+   */
+  void *cont_cls;
+
+};
+
+
+/**
+ * Context for processing result messages.
+ */
+struct ResultContext
+{
+  /**
+   * Function to call with the result.
+   */
+  GNUNET_DATASTORE_DatumProcessor proc;
+
+  /**
+   * Closure for proc.
+   */
+  void *proc_cls;
+
+};
+
+
+/**
+ *  Context for a queue operation.
+ */
+union QueueContext
+{
+
+  struct StatusContext sc;
+
+  struct ResultContext rc;
+
+};
+
+
+
+/**
+ * Entry in our priority queue.
+ */
+struct GNUNET_DATASTORE_QueueEntry
+{
+
+  /**
+   * This is a linked list.
+   */
+  struct GNUNET_DATASTORE_QueueEntry *next;
+
+  /**
+   * This is a linked list.
+   */
+  struct GNUNET_DATASTORE_QueueEntry *prev;
+
+  /**
+   * Handle to the master context.
+   */
+  struct GNUNET_DATASTORE_Handle *h;
+
+  /**
+   * Response processor (NULL if we are not waiting for a response).
+   * This struct should be used for the closure, function-specific
+   * arguments can be passed via 'qc'.
+   */
+  GNUNET_CLIENT_MessageHandler response_proc;
+
+  /**
+   * Function to call after transmission of the request.
+   */
+  GNUNET_DATASTORE_ContinuationWithStatus cont;
+
+  /**
+   * Closure for 'cont'.
+   */
+  void *cont_cls;
+
+  /**
+   * Context for the operation.
+   */
+  union QueueContext qc;
+
+  /**
+   * Task for timeout signalling.
+   */
+  GNUNET_SCHEDULER_TaskIdentifier task;
+
+  /**
+   * Timeout for the current operation.
+   */
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * Priority in the queue.
+   */
+  unsigned int priority;
+
+  /**
+   * Maximum allowed length of queue (otherwise
+   * this request should be discarded).
+   */
+  unsigned int max_queue;
+
+  /**
+   * Number of bytes in the request message following
+   * this struct.  32-bit value for nicer memory
+   * access (and overall struct alignment).
+   */
+  uint32_t message_size;
+
+  /**
+   * Has this message been transmitted to the service?
+   * Only ever GNUNET_YES for the head of the queue.
+   * Note that the overall struct should end at a 
+   * multiple of 64 bits.
+   */
+  int was_transmitted;
+
+};
+
+/**
+ * Handle to the datastore service. 
  */
 struct GNUNET_DATASTORE_Handle
 {
@@ -40,93 +182,118 @@ struct GNUNET_DATASTORE_Handle
   const struct GNUNET_CONFIGURATION_Handle *cfg;
 
   /**
-   * Our scheduler.
+   * Current connection to the datastore service.
    */
-  struct GNUNET_SCHEDULER_Handle *sched;
+  struct GNUNET_CLIENT_Connection *client;
 
   /**
-   * Current connection to the datastore service.
+   * Handle for statistics.
    */
-  struct GNUNET_CLIENT_Connection *client;
+  struct GNUNET_STATISTICS_Handle *stats;
 
   /**
-   * Current response processor (NULL if we are not waiting for a
-   * response).  The specific type depends on the kind of message we
-   * just transmitted.
+   * Current transmit handle.
    */
-  void *response_proc;
-  
+  struct GNUNET_CLIENT_TransmitHandle *th;
+
   /**
-   * Closure for response_proc.
+   * Current head of priority queue.
    */
-  void *response_proc_cls;
+  struct GNUNET_DATASTORE_QueueEntry *queue_head;
 
   /**
-   * Timeout for the current operation.
+   * Current tail of priority queue.
    */
-  struct GNUNET_TIME_Absolute timeout;
+  struct GNUNET_DATASTORE_QueueEntry *queue_tail;
+
+  /**
+   * Task for trying to reconnect.
+   */
+  GNUNET_SCHEDULER_TaskIdentifier reconnect_task;
+
+  /**
+   * How quickly should we retry?  Used for exponential back-off on
+   * connect-errors.
+   */
+  struct GNUNET_TIME_Relative retry_time;
+
+  /**
+   * Number of entries in the queue.
+   */
+  unsigned int queue_size;
+
+  /**
+   * Number of results we're receiving for the current query
+   * after application stopped to care.  Used to determine when
+   * to reset the connection.
+   */
+  unsigned int result_count;
+
+  /**
+   * Are we currently trying to receive from the service?
+   */
+  int in_receive;
 
   /**
-   * Number of bytes in the message following
-   * this struct, 0 if we have no request pending.
+   * We should ignore the next message(s) from the service.
    */
-  size_t message_size;
+  unsigned int skip_next_messages;
 
 };
 
 
+
 /**
  * Connect to the datastore service.
  *
  * @param cfg configuration to use
- * @param sched scheduler to use
  * @return handle to use to access the service
  */
-struct GNUNET_DATASTORE_Handle *GNUNET_DATASTORE_connect (const struct
-                                                          GNUNET_CONFIGURATION_Handle
-                                                          *cfg,
-                                                          struct
-                                                          GNUNET_SCHEDULER_Handle
-                                                          *sched)
+struct GNUNET_DATASTORE_Handle *
+GNUNET_DATASTORE_connect (const struct GNUNET_CONFIGURATION_Handle *cfg)
 {
   struct GNUNET_CLIENT_Connection *c;
   struct GNUNET_DATASTORE_Handle *h;
-  
-  c = GNUNET_CLIENT_connect (sched, "datastore", cfg);
+
+  c = GNUNET_CLIENT_connect ("datastore", cfg);
   if (c == NULL)
-    return NULL; /* oops */
-  h = GNUNET_malloc (sizeof(struct GNUNET_DATASTORE_Handle) + 
-		     GNUNET_SERVER_MAX_MESSAGE_SIZE);
+    return NULL;                /* oops */
+  h = GNUNET_malloc (sizeof (struct GNUNET_DATASTORE_Handle) +
+                     GNUNET_SERVER_MAX_MESSAGE_SIZE - 1);
   h->client = c;
   h->cfg = cfg;
-  h->sched = sched;
+  h->stats = GNUNET_STATISTICS_create ("datastore-api", cfg);
   return h;
 }
 
 
 /**
  * Transmit DROP message to datastore service.
+ *
+ * @param cls the 'struct GNUNET_DATASTORE_Handle'
+ * @param size number of bytes that can be copied to buf
+ * @param buf where to copy the drop message
+ * @return number of bytes written to buf
  */
 static size_t
-transmit_drop (void *cls,
-	       size_t size, void *buf)
+transmit_drop (void *cls, size_t size, void *buf)
 {
   struct GNUNET_DATASTORE_Handle *h = cls;
   struct GNUNET_MessageHeader *hdr;
-  
+
   if (buf == NULL)
-    {
-      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
-		  _("Failed to transmit request to drop database.\n"));
-      GNUNET_DATASTORE_disconnect (h, GNUNET_NO);
-      return 0;
-    }
-  GNUNET_assert (size >= sizeof(struct GNUNET_MessageHeader));
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                _("Failed to transmit request to drop database.\n"));
+    GNUNET_DATASTORE_disconnect (h, GNUNET_NO);
+    return 0;
+  }
+  GNUNET_assert (size >= sizeof (struct GNUNET_MessageHeader));
   hdr = buf;
-  hdr->size = htons(sizeof(struct GNUNET_MessageHeader));
-  hdr->type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_DROP);
+  hdr->size = htons (sizeof (struct GNUNET_MessageHeader));
+  hdr->type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_DROP);
   GNUNET_DATASTORE_disconnect (h, GNUNET_NO);
-  return sizeof(struct GNUNET_MessageHeader);
+  return sizeof (struct GNUNET_MessageHeader);
 }
 
 
@@ -137,195 +304,510 @@ transmit_drop (void *cls,
  * @param h handle to the datastore
  * @param drop set to GNUNET_YES to delete all data in datastore (!)
  */
-void GNUNET_DATASTORE_disconnect (struct GNUNET_DATASTORE_Handle *h,
-				  int drop)
+void
+GNUNET_DATASTORE_disconnect (struct GNUNET_DATASTORE_Handle *h, int drop)
 {
-  GNUNET_assert (0 == h->message_size);
-  GNUNET_assert (NULL == h->response_proc);
-  if ( (GNUNET_YES == drop) &&
-       (h->client != NULL) )
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Datastore disconnect\n");
+#endif
+  if (NULL != h->th)
+  {
+    GNUNET_CLIENT_notify_transmit_ready_cancel (h->th);
+    h->th = NULL;
+  }
+  if (h->client != NULL)
+  {
+    GNUNET_CLIENT_disconnect (h->client, GNUNET_NO);
+    h->client = NULL;
+  }
+  if (h->reconnect_task != GNUNET_SCHEDULER_NO_TASK)
+  {
+    GNUNET_SCHEDULER_cancel (h->reconnect_task);
+    h->reconnect_task = GNUNET_SCHEDULER_NO_TASK;
+  }
+  while (NULL != (qe = h->queue_head))
+  {
+    GNUNET_assert (NULL != qe->response_proc);
+    qe->response_proc (h, NULL);
+  }
+  if (GNUNET_YES == drop)
+  {
+    h->client = GNUNET_CLIENT_connect ("datastore", h->cfg);
+    if (h->client != NULL)
     {
-      if (NULL != 
-	  GNUNET_CLIENT_notify_transmit_ready (h->client,
-					       sizeof(struct GNUNET_MessageHeader),
-					       GNUNET_TIME_UNIT_MINUTES,
-					       &transmit_drop,
-					       h))
-	return;
-      GNUNET_break (0);
+      if (NULL !=
+          GNUNET_CLIENT_notify_transmit_ready (h->client,
+                                               sizeof (struct
+                                                       GNUNET_MessageHeader),
+                                               GNUNET_TIME_UNIT_MINUTES,
+                                               GNUNET_YES, &transmit_drop, h))
+        return;
+      GNUNET_CLIENT_disconnect (h->client, GNUNET_NO);
+      h->client = NULL;
     }
-  if (h->client != NULL)
-    GNUNET_CLIENT_disconnect (h->client);
+    GNUNET_break (0);
+  }
+  GNUNET_STATISTICS_destroy (h->stats, GNUNET_NO);
+  h->stats = NULL;
   GNUNET_free (h);
 }
 
 
 /**
- * Type of a function to call when we receive a message
- * from the service.  This specific function is used
- * to handle messages of type "struct StatusMessage".
+ * A request has timed out (before being transmitted to the service).
  *
- * @param cls closure
- * @param msg message received, NULL on timeout or fatal error
+ * @param cls the 'struct GNUNET_DATASTORE_QueueEntry'
+ * @param tc scheduler context
  */
-static void 
-with_status_response_handler (void *cls,
-			      const struct
-			      GNUNET_MessageHeader * msg)
+static void
+timeout_queue_entry (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
 {
-  struct GNUNET_DATASTORE_Handle *h = cls;
-  GNUNET_DATASTORE_ContinuationWithStatus cont = h->response_proc;
-  const struct StatusMessage *sm;
-  const char *emsg;
-  int status;
+  struct GNUNET_DATASTORE_QueueEntry *qe = cls;
 
-  if (msg == NULL)
-    {
-      h->response_proc = NULL;
-      GNUNET_CLIENT_disconnect (h->client);
-      h->client = GNUNET_CLIENT_connect (h->sched, "datastore", h->cfg);
-      cont (h->response_proc_cls, 
-	    GNUNET_SYSERR,
-	    _("Timeout trying to read response from datastore service\n"));       
-      return;
-    }
-  if ( (ntohs(msg->size) < sizeof(struct StatusMessage)) ||
-       (ntohs(msg->type) != GNUNET_MESSAGE_TYPE_DATASTORE_STATUS) ) 
-    {
-      GNUNET_break (0);
-      h->response_proc = NULL;
-      GNUNET_CLIENT_disconnect (h->client);
-      h->client = GNUNET_CLIENT_connect (h->sched, "datastore", h->cfg);
-      cont (h->response_proc_cls, 
-	    GNUNET_SYSERR,
-	    _("Error reading response from datastore service\n"));
-      return;
-    }
-  sm = (const struct StatusMessage*) msg;
-  status = ntohl(sm->status);
-  emsg = NULL;
-  if (ntohs(msg->size) > sizeof(struct StatusMessage))
-    {
-      emsg = (const char*) &sm[1];
-      if (emsg[ntohs(msg->size) - sizeof(struct StatusMessage) - 1] != '\0')
-	{
-	  GNUNET_break (0);
-	  emsg = _("Invalid error message received from datastore service");
-	}
-    }  
-  if ( (status == GNUNET_SYSERR) &&
-       (emsg == NULL) )
+  GNUNET_STATISTICS_update (qe->h->stats,
+                            gettext_noop ("# queue entry timeouts"), 1,
+                            GNUNET_NO);
+  qe->task = GNUNET_SCHEDULER_NO_TASK;
+  GNUNET_assert (qe->was_transmitted == GNUNET_NO);
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Timeout of request in datastore queue\n");
+#endif
+  qe->response_proc (qe->h, NULL);
+}
+
+
+/**
+ * Create a new entry for our priority queue (and possibly discard other entires if
+ * the queue is getting too long).
+ *
+ * @param h handle to the datastore
+ * @param msize size of the message to queue
+ * @param queue_priority priority of the entry
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout timeout for the operation
+ * @param response_proc function to call with replies (can be NULL)
+ * @param qc client context (NOT a closure for response_proc)
+ * @return NULL if the queue is full 
+ */
+static struct GNUNET_DATASTORE_QueueEntry *
+make_queue_entry (struct GNUNET_DATASTORE_Handle *h, size_t msize,
+                  unsigned int queue_priority, unsigned int max_queue_size,
+                  struct GNUNET_TIME_Relative timeout,
+                  GNUNET_CLIENT_MessageHandler response_proc,
+                  const union QueueContext *qc)
+{
+  struct GNUNET_DATASTORE_QueueEntry *ret;
+  struct GNUNET_DATASTORE_QueueEntry *pos;
+  unsigned int c;
+
+  c = 0;
+  pos = h->queue_head;
+  while ((pos != NULL) && (c < max_queue_size) &&
+         (pos->priority >= queue_priority))
+  {
+    c++;
+    pos = pos->next;
+  }
+  if (c >= max_queue_size)
+  {
+    GNUNET_STATISTICS_update (h->stats, gettext_noop ("# queue overflows"), 1,
+                              GNUNET_NO);
+    return NULL;
+  }
+  ret = GNUNET_malloc (sizeof (struct GNUNET_DATASTORE_QueueEntry) + msize);
+  ret->h = h;
+  ret->response_proc = response_proc;
+  ret->qc = *qc;
+  ret->timeout = GNUNET_TIME_relative_to_absolute (timeout);
+  ret->priority = queue_priority;
+  ret->max_queue = max_queue_size;
+  ret->message_size = msize;
+  ret->was_transmitted = GNUNET_NO;
+  if (pos == NULL)
+  {
+    /* append at the tail */
+    pos = h->queue_tail;
+  }
+  else
+  {
+    pos = pos->prev;
+    /* do not insert at HEAD if HEAD query was already
+     * transmitted and we are still receiving replies! */
+    if ((pos == NULL) && (h->queue_head->was_transmitted))
+      pos = h->queue_head;
+  }
+  c++;
+  GNUNET_STATISTICS_update (h->stats, gettext_noop ("# queue entries created"),
+                            1, GNUNET_NO);
+  GNUNET_CONTAINER_DLL_insert_after (h->queue_head, h->queue_tail, pos, ret);
+  h->queue_size++;
+  ret->task = GNUNET_SCHEDULER_add_delayed (timeout, &timeout_queue_entry, ret);
+  pos = ret->next;
+  while (pos != NULL)
+  {
+    if ((pos->max_queue < h->queue_size) && (pos->was_transmitted == GNUNET_NO))
     {
-      GNUNET_break (0);
-      emsg = _("Invalid error message received from datastore service");
+      GNUNET_assert (pos->response_proc != NULL);
+      /* move 'pos' element to head so that it will be 
+       * killed on 'NULL' call below */
+#if DEBUG_DATASTORE
+      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                  "Dropping request from datastore queue\n");
+#endif
+      GNUNET_CONTAINER_DLL_remove (h->queue_head, h->queue_tail, pos);
+      GNUNET_CONTAINER_DLL_insert (h->queue_head, h->queue_tail, pos);
+      GNUNET_STATISTICS_update (h->stats,
+                                gettext_noop
+                                ("# Requests dropped from datastore queue"), 1,
+                                GNUNET_NO);
+      GNUNET_assert (h->queue_head == pos);
+      pos->response_proc (h, NULL);
+      break;
     }
-  h->response_proc = NULL;
+    pos = pos->next;
+  }
+  return ret;
+}
+
+
+/**
+ * Process entries in the queue (or do nothing if we are already
+ * doing so).
+ * 
+ * @param h handle to the datastore
+ */
+static void process_queue (struct GNUNET_DATASTORE_Handle *h);
+
+
+/**
+ * Try reconnecting to the datastore service.
+ *
+ * @param cls the 'struct GNUNET_DATASTORE_Handle'
+ * @param tc scheduler context
+ */
+static void
+try_reconnect (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
+{
+  struct GNUNET_DATASTORE_Handle *h = cls;
+
+  if (h->retry_time.rel_value < GNUNET_CONSTANTS_SERVICE_RETRY.rel_value)
+    h->retry_time = GNUNET_CONSTANTS_SERVICE_RETRY;
+  else
+    h->retry_time = GNUNET_TIME_relative_multiply (h->retry_time, 2);
+  if (h->retry_time.rel_value > GNUNET_CONSTANTS_SERVICE_TIMEOUT.rel_value)
+    h->retry_time = GNUNET_CONSTANTS_SERVICE_TIMEOUT;
+  h->reconnect_task = GNUNET_SCHEDULER_NO_TASK;
+  h->client = GNUNET_CLIENT_connect ("datastore", h->cfg);
+  if (h->client == NULL)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "DATASTORE reconnect failed (fatally)\n");
+    return;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop
+                            ("# datastore connections (re)created"), 1,
+                            GNUNET_NO);
 #if DEBUG_DATASTORE
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Received status %d/%s\n",
-	      status,
-	      emsg);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Reconnected to DATASTORE\n");
 #endif
-  cont (h->response_proc_cls, 
-	status,
-	emsg);
+  process_queue (h);
 }
 
 
 /**
- * Transmit message to datastore service and then
- * read a status message.
+ * Disconnect from the service and then try reconnecting to the datastore service
+ * after some delay.
  *
- * @param cls closure with handle to datastore
- * @param size number of bytes we can transmit at most
- * @param buf where to write transmission, NULL on
- *        timeout
- * @return number of bytes copied to buf
+ * @param h handle to datastore to disconnect and reconnect
+ */
+static void
+do_disconnect (struct GNUNET_DATASTORE_Handle *h)
+{
+  if (h->client == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "client NULL in disconnect, will not try to reconnect\n");
+#endif
+    return;
+  }
+#if 0
+  GNUNET_STATISTICS_update (stats, gettext_noop ("# reconnected to DATASTORE"),
+                            1, GNUNET_NO);
+#endif
+  GNUNET_CLIENT_disconnect (h->client, GNUNET_NO);
+  h->skip_next_messages = 0;
+  h->client = NULL;
+  h->reconnect_task =
+      GNUNET_SCHEDULER_add_delayed (h->retry_time, &try_reconnect, h);
+}
+
+
+/**
+ * Function called whenever we receive a message from
+ * the service.  Calls the appropriate handler.
+ *
+ * @param cls the 'struct GNUNET_DATASTORE_Handle'
+ * @param msg the received message
+ */
+static void
+receive_cb (void *cls, const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_DATASTORE_Handle *h = cls;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+
+  h->in_receive = GNUNET_NO;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Receiving reply from datastore\n");
+#endif
+  if (h->skip_next_messages > 0)
+  {
+    h->skip_next_messages--;
+    process_queue (h);
+    return;
+  }
+  if (NULL == (qe = h->queue_head))
+  {
+    GNUNET_break (0);
+    process_queue (h);
+    return;
+  }
+  qe->response_proc (h, msg);
+}
+
+
+/**
+ * Transmit request from queue to datastore service.
+ *
+ * @param cls the 'struct GNUNET_DATASTORE_Handle'
+ * @param size number of bytes that can be copied to buf
+ * @param buf where to copy the drop message
+ * @return number of bytes written to buf
  */
 static size_t
-transmit_get_status (void *cls,
-		     size_t size,
-		     void *buf)
+transmit_request (void *cls, size_t size, void *buf)
 {
   struct GNUNET_DATASTORE_Handle *h = cls;
-  GNUNET_DATASTORE_ContinuationWithStatus cont = h->response_proc;
-  uint16_t msize;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  size_t msize;
 
+  h->th = NULL;
+  if (NULL == (qe = h->queue_head))
+    return 0;                   /* no entry in queue */
   if (buf == NULL)
-    {
-      h->message_size = 0;
-      h->response_proc = NULL;
-      cont (h->response_proc_cls, 
-	    GNUNET_SYSERR,
-	    gettext_noop ("Error transmitting message to datastore service.\n"));
-      return 0;
-    }
-  msize = h->message_size;
-  GNUNET_assert (msize <= size);
-  memcpy (buf, &h[1], msize);
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                _("Failed to transmit request to DATASTORE.\n"));
+    GNUNET_STATISTICS_update (h->stats,
+                              gettext_noop ("# transmission request failures"),
+                              1, GNUNET_NO);
+    do_disconnect (h);
+    return 0;
+  }
+  if (size < (msize = qe->message_size))
+  {
+    process_queue (h);
+    return 0;
+  }
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Transmitted %u byte message to datastore service, now waiting for status.\n",
-	      msize);
-#endif
-  h->message_size = 0;
-  GNUNET_CLIENT_receive (h->client,
-			 &with_status_response_handler,
-			 h,
-			 GNUNET_TIME_absolute_get_remaining (h->timeout));
+              "Transmitting %u byte request to DATASTORE\n", msize);
+#endif
+  memcpy (buf, &qe[1], msize);
+  qe->was_transmitted = GNUNET_YES;
+  GNUNET_SCHEDULER_cancel (qe->task);
+  qe->task = GNUNET_SCHEDULER_NO_TASK;
+  GNUNET_assert (GNUNET_NO == h->in_receive);
+  h->in_receive = GNUNET_YES;
+  GNUNET_CLIENT_receive (h->client, &receive_cb, h,
+                         GNUNET_TIME_absolute_get_remaining (qe->timeout));
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop ("# bytes sent to datastore"), 1,
+                            GNUNET_NO);
   return msize;
 }
 
 
 /**
- * Helper function that will initiate the
- * transmission of a message to the datastore
- * service.  The message must already be prepared
- * and stored in the buffer at the end of the
- * handle.  The message must be of a type that
- * expects a "StatusMessage" in response.
- *
- * @param h handle to the service with prepared message
- * @param cont function to call with result
- * @param cont_cls closure
- * @param timeout timeout for the operation
+ * Process entries in the queue (or do nothing if we are already
+ * doing so).
+ * 
+ * @param h handle to the datastore
  */
 static void
-transmit_for_status (struct GNUNET_DATASTORE_Handle *h,
-		     GNUNET_DATASTORE_ContinuationWithStatus cont,
-		     void *cont_cls,
-		     struct GNUNET_TIME_Relative timeout)
+process_queue (struct GNUNET_DATASTORE_Handle *h)
 {
-  const struct GNUNET_MessageHeader *hdr;
-  uint16_t msize;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
 
-  GNUNET_assert (cont != NULL);
-  hdr = (const struct GNUNET_MessageHeader*) &h[1];
-  msize = ntohs(hdr->size);
+  if (NULL == (qe = h->queue_head))
+  {
+#if DEBUG_DATASTORE > 1
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Queue empty\n");
+#endif
+    return;                     /* no entry in queue */
+  }
+  if (qe->was_transmitted == GNUNET_YES)
+  {
+#if DEBUG_DATASTORE > 1
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Head request already transmitted\n");
+#endif
+    return;                     /* waiting for replies */
+  }
+  if (h->th != NULL)
+  {
+#if DEBUG_DATASTORE > 1
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Pending transmission request\n");
+#endif
+    return;                     /* request pending */
+  }
+  if (h->client == NULL)
+  {
+#if DEBUG_DATASTORE > 1
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Not connected\n");
+#endif
+    return;                     /* waiting for reconnect */
+  }
+  if (GNUNET_YES == h->in_receive)
+  {
+    /* wait for response to previous query */
+    return;
+  }
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Transmitting %u byte message of type %u to datastore service\n",
-	      msize,
-	      ntohs(hdr->type));
-#endif
-  GNUNET_assert (h->response_proc == NULL);
-  h->response_proc = cont;
-  h->response_proc_cls = cont_cls;
-  h->timeout = GNUNET_TIME_relative_to_absolute (timeout);
-  h->message_size = msize;
-  if (NULL == GNUNET_CLIENT_notify_transmit_ready (h->client,
-						   msize,
-						   timeout,
-						   &transmit_get_status,
-						   h))
+              "Queueing %u byte request to DATASTORE\n", qe->message_size);
+#endif
+  h->th =
+      GNUNET_CLIENT_notify_transmit_ready (h->client, qe->message_size,
+                                           GNUNET_TIME_absolute_get_remaining
+                                           (qe->timeout), GNUNET_YES,
+                                           &transmit_request, h);
+  GNUNET_assert (GNUNET_NO == h->in_receive);
+  GNUNET_break (NULL != h->th);
+}
+
+
+/**
+ * Dummy continuation used to do nothing (but be non-zero).
+ *
+ * @param cls closure
+ * @param result result 
+ * @param emsg error message
+ */
+static void
+drop_status_cont (void *cls, int32_t result, const char *emsg)
+{
+  /* do nothing */
+}
+
+
+/**
+ * Free a queue entry.  Removes the given entry from the
+ * queue and releases associated resources.  Does NOT
+ * call the callback.
+ * 
+ * @param qe entry to free.
+ */
+static void
+free_queue_entry (struct GNUNET_DATASTORE_QueueEntry *qe)
+{
+  struct GNUNET_DATASTORE_Handle *h = qe->h;
+
+  GNUNET_CONTAINER_DLL_remove (h->queue_head, h->queue_tail, qe);
+  if (qe->task != GNUNET_SCHEDULER_NO_TASK)
+  {
+    GNUNET_SCHEDULER_cancel (qe->task);
+    qe->task = GNUNET_SCHEDULER_NO_TASK;
+  }
+  h->queue_size--;
+  qe->was_transmitted = GNUNET_SYSERR;  /* use-after-free warning */
+  GNUNET_free (qe);
+}
+
+
+/**
+ * Type of a function to call when we receive a message
+ * from the service.
+ *
+ * @param cls closure
+ * @param msg message received, NULL on timeout or fatal error
+ */
+static void
+process_status_message (void *cls, const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_DATASTORE_Handle *h = cls;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  struct StatusContext rc;
+  const struct StatusMessage *sm;
+  const char *emsg;
+  int32_t status;
+  int was_transmitted;
+
+  if (NULL == (qe = h->queue_head))
+  {
+    GNUNET_break (0);
+    do_disconnect (h);
+    return;
+  }
+  rc = qe->qc.sc;
+  if (msg == NULL)
+  {
+    was_transmitted = qe->was_transmitted;
+    free_queue_entry (qe);
+    if (was_transmitted == GNUNET_YES)
+      do_disconnect (h);
+    else
+      process_queue (h);
+    if (rc.cont != NULL)
+      rc.cont (rc.cont_cls, GNUNET_SYSERR,
+               _("Failed to receive status response from database."));
+    return;
+  }
+  GNUNET_assert (GNUNET_YES == qe->was_transmitted);
+  free_queue_entry (qe);
+  if ((ntohs (msg->size) < sizeof (struct StatusMessage)) ||
+      (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_DATASTORE_STATUS))
+  {
+    GNUNET_break (0);
+    h->retry_time = GNUNET_TIME_UNIT_ZERO;
+    do_disconnect (h);
+    if (rc.cont != NULL)
+      rc.cont (rc.cont_cls, GNUNET_SYSERR,
+               _("Error reading response from datastore service"));
+    return;
+  }
+  sm = (const struct StatusMessage *) msg;
+  status = ntohl (sm->status);
+  emsg = NULL;
+  if (ntohs (msg->size) > sizeof (struct StatusMessage))
+  {
+    emsg = (const char *) &sm[1];
+    if (emsg[ntohs (msg->size) - sizeof (struct StatusMessage) - 1] != '\0')
     {
       GNUNET_break (0);
-      h->response_proc = NULL;
-      h->message_size = 0;
-      cont (cont_cls,
-	    GNUNET_SYSERR,
-	    gettext_noop ("Not ready to transmit request to datastore service"));
+      emsg = _("Invalid error message received from datastore service");
     }
+  }
+  if ((status == GNUNET_SYSERR) && (emsg == NULL))
+  {
+    GNUNET_break (0);
+    emsg = _("Invalid error message received from datastore service");
+  }
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Received status %d/%s\n", (int) status,
+              emsg);
+#endif
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop ("# status messages received"), 1,
+                            GNUNET_NO);
+  h->retry_time.rel_value = 0;
+  process_queue (h);
+  if (rc.cont != NULL)
+    rc.cont (rc.cont_cls, status, emsg);
 }
 
 
@@ -335,54 +817,81 @@ transmit_for_status (struct GNUNET_DATASTORE_Handle *h,
  * lower anonymity level is used.
  *
  * @param h handle to the datastore
+ * @param rid reservation ID to use (from "reserve"); use 0 if no
+ *            prior reservation was made
  * @param key key for the value
  * @param size number of bytes in data
  * @param data content stored
  * @param type type of the content
  * @param priority priority of the content
  * @param anonymity anonymity-level for the content
+ * @param replication how often should the content be replicated to other peers?
  * @param expiration expiration time for the content
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
  * @param timeout timeout for the operation
  * @param cont continuation to call when done
  * @param cont_cls closure for cont
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel; note that even if NULL is returned, the callback will be invoked
+ *         (or rather, will already have been invoked)
  */
-void
-GNUNET_DATASTORE_put (struct GNUNET_DATASTORE_Handle *h,
-		      int rid,
-                      const GNUNET_HashCode * key,
-                      uint32_t size,
-                      const void *data,
-                      uint32_t type,
-                      uint32_t priority,
-                      uint32_t anonymity,
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_put (struct GNUNET_DATASTORE_Handle *h, uint32_t rid,
+                      const GNUNET_HashCode * key, size_t size,
+                      const void *data, enum GNUNET_BLOCK_Type type,
+                      uint32_t priority, uint32_t anonymity,
+                      uint32_t replication,
                       struct GNUNET_TIME_Absolute expiration,
+                      unsigned int queue_priority, unsigned int max_queue_size,
                       struct GNUNET_TIME_Relative timeout,
-		      GNUNET_DATASTORE_ContinuationWithStatus cont,
-		      void *cont_cls)
+                      GNUNET_DATASTORE_ContinuationWithStatus cont,
+                      void *cont_cls)
 {
+  struct GNUNET_DATASTORE_QueueEntry *qe;
   struct DataMessage *dm;
   size_t msize;
+  union QueueContext qc;
 
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Asked to put %u bytes of data\n",
-	      size);
-#endif
-  msize = sizeof(struct DataMessage) + size;
-  GNUNET_assert (msize <= GNUNET_SERVER_MAX_MESSAGE_SIZE);
-  dm = (struct DataMessage*) &h[1];
-  dm->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_PUT);
-  dm->header.size = htons(msize);
-  dm->rid = htonl(rid);
-  dm->size = htonl(size);
-  dm->type = htonl(type);
-  dm->priority = htonl(priority);
-  dm->anonymity = htonl(anonymity);
-  dm->uid = GNUNET_htonll(0);
-  dm->expiration = GNUNET_TIME_absolute_hton(expiration);
+              "Asked to put %u bytes of data under key `%s' for %llu ms\n",
+              size, GNUNET_h2s (key),
+              GNUNET_TIME_absolute_get_remaining (expiration).rel_value);
+#endif
+  msize = sizeof (struct DataMessage) + size;
+  GNUNET_assert (msize < GNUNET_SERVER_MAX_MESSAGE_SIZE);
+  qc.sc.cont = cont;
+  qc.sc.cont_cls = cont_cls;
+  qe = make_queue_entry (h, msize, queue_priority, max_queue_size, timeout,
+                         &process_status_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry for PUT\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats, gettext_noop ("# PUT requests executed"),
+                            1, GNUNET_NO);
+  dm = (struct DataMessage *) &qe[1];
+  dm->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_PUT);
+  dm->header.size = htons (msize);
+  dm->rid = htonl (rid);
+  dm->size = htonl ((uint32_t) size);
+  dm->type = htonl (type);
+  dm->priority = htonl (priority);
+  dm->anonymity = htonl (anonymity);
+  dm->replication = htonl (replication);
+  dm->reserved = htonl (0);
+  dm->uid = GNUNET_htonll (0);
+  dm->expiration = GNUNET_TIME_absolute_hton (expiration);
   dm->key = *key;
   memcpy (&dm[1], data, size);
-  transmit_for_status (h, cont, cont_cls, timeout);
+  process_queue (h);
+  return qe;
 }
 
 
@@ -394,27 +903,58 @@ GNUNET_DATASTORE_put (struct GNUNET_DATASTORE_Handle *h,
  * @param h handle to the datastore
  * @param amount how much space (in bytes) should be reserved (for content only)
  * @param entries how many entries will be created (to calculate per-entry overhead)
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response (or before dying in queue)
  * @param cont continuation to call when done; "success" will be set to
  *             a positive reservation value if space could be reserved.
  * @param cont_cls closure for cont
- * @param timeout how long to wait at most for a response
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel; note that even if NULL is returned, the callback will be invoked
+ *         (or rather, will already have been invoked)
  */
-void
-GNUNET_DATASTORE_reserve (struct GNUNET_DATASTORE_Handle *h,
-			  uint64_t amount,
-			  uint32_t entries,
-			  GNUNET_DATASTORE_ContinuationWithStatus cont,
-			  void *cont_cls,
-			  struct GNUNET_TIME_Relative timeout)
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_reserve (struct GNUNET_DATASTORE_Handle *h, uint64_t amount,
+                          uint32_t entries, unsigned int queue_priority,
+                          unsigned int max_queue_size,
+                          struct GNUNET_TIME_Relative timeout,
+                          GNUNET_DATASTORE_ContinuationWithStatus cont,
+                          void *cont_cls)
 {
+  struct GNUNET_DATASTORE_QueueEntry *qe;
   struct ReserveMessage *rm;
+  union QueueContext qc;
 
-  rm = (struct ReserveMessage*) &h[1];
-  rm->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_RESERVE);
-  rm->header.size = htons(sizeof (struct ReserveMessage));
-  rm->entries = htonl(entries);
-  rm->amount = GNUNET_htonll(amount);
-  transmit_for_status (h, cont, cont_cls, timeout);
+  if (cont == NULL)
+    cont = &drop_status_cont;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Asked to reserve %llu bytes of data and %u entries\n",
+              (unsigned long long) amount, (unsigned int) entries);
+#endif
+  qc.sc.cont = cont;
+  qc.sc.cont_cls = cont_cls;
+  qe = make_queue_entry (h, sizeof (struct ReserveMessage), queue_priority,
+                         max_queue_size, timeout, &process_status_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry to reserve\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop ("# RESERVE requests executed"), 1,
+                            GNUNET_NO);
+  rm = (struct ReserveMessage *) &qe[1];
+  rm->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_RESERVE);
+  rm->header.size = htons (sizeof (struct ReserveMessage));
+  rm->entries = htonl (entries);
+  rm->amount = GNUNET_htonll (amount);
+  process_queue (h);
+  return qe;
 }
 
 
@@ -426,24 +966,59 @@ GNUNET_DATASTORE_reserve (struct GNUNET_DATASTORE_Handle *h,
  * @param h handle to the datastore
  * @param rid reservation ID (value of "success" in original continuation
  *        from the "reserve" function).
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response
  * @param cont continuation to call when done
  * @param cont_cls closure for cont
- * @param timeout how long to wait at most for a response
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel; note that even if NULL is returned, the callback will be invoked
+ *         (or rather, will already have been invoked)
  */
-void
+struct GNUNET_DATASTORE_QueueEntry *
 GNUNET_DATASTORE_release_reserve (struct GNUNET_DATASTORE_Handle *h,
-				  int rid,
-				  GNUNET_DATASTORE_ContinuationWithStatus cont,
-				  void *cont_cls,
-				  struct GNUNET_TIME_Relative timeout)
+                                  uint32_t rid, unsigned int queue_priority,
+                                  unsigned int max_queue_size,
+                                  struct GNUNET_TIME_Relative timeout,
+                                  GNUNET_DATASTORE_ContinuationWithStatus cont,
+                                  void *cont_cls)
 {
+  struct GNUNET_DATASTORE_QueueEntry *qe;
   struct ReleaseReserveMessage *rrm;
+  union QueueContext qc;
 
-  rrm = (struct ReleaseReserveMessage*) &h[1];
-  rrm->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_RELEASE_RESERVE);
-  rrm->header.size = htons(sizeof (struct ReleaseReserveMessage));
-  rrm->rid = htonl(rid);
-  transmit_for_status (h, cont, cont_cls, timeout);
+  if (cont == NULL)
+    cont = &drop_status_cont;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Asked to release reserve %d\n", rid);
+#endif
+  qc.sc.cont = cont;
+  qc.sc.cont_cls = cont_cls;
+  qe = make_queue_entry (h, sizeof (struct ReleaseReserveMessage),
+                         queue_priority, max_queue_size, timeout,
+                         &process_status_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry to release reserve\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop
+                            ("# RELEASE RESERVE requests executed"), 1,
+                            GNUNET_NO);
+  rrm = (struct ReleaseReserveMessage *) &qe[1];
+  rrm->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_RELEASE_RESERVE);
+  rrm->header.size = htons (sizeof (struct ReleaseReserveMessage));
+  rrm->rid = htonl (rid);
+  process_queue (h);
+  return qe;
 }
 
 
@@ -454,315 +1029,477 @@ GNUNET_DATASTORE_release_reserve (struct GNUNET_DATASTORE_Handle *h,
  * @param uid identifier for the value
  * @param priority how much to increase the priority of the value
  * @param expiration new expiration value should be MAX of existing and this argument
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response
  * @param cont continuation to call when done
  * @param cont_cls closure for cont
- * @param timeout how long to wait at most for a response
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel; note that even if NULL is returned, the callback will be invoked
+ *         (or rather, will already have been invoked)
  */
-void
-GNUNET_DATASTORE_update (struct GNUNET_DATASTORE_Handle *h,
-			 unsigned long long uid,
-			 uint32_t priority,
-			 struct GNUNET_TIME_Absolute expiration,
-			 GNUNET_DATASTORE_ContinuationWithStatus cont,
-			 void *cont_cls,
-			 struct GNUNET_TIME_Relative timeout)
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_update (struct GNUNET_DATASTORE_Handle *h, uint64_t uid,
+                         uint32_t priority,
+                         struct GNUNET_TIME_Absolute expiration,
+                         unsigned int queue_priority,
+                         unsigned int max_queue_size,
+                         struct GNUNET_TIME_Relative timeout,
+                         GNUNET_DATASTORE_ContinuationWithStatus cont,
+                         void *cont_cls)
 {
+  struct GNUNET_DATASTORE_QueueEntry *qe;
   struct UpdateMessage *um;
+  union QueueContext qc;
 
-  um = (struct UpdateMessage*) &h[1];
-  um->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_UPDATE);
-  um->header.size = htons(sizeof (struct UpdateMessage));
-  um->priority = htonl(priority);
-  um->expiration = GNUNET_TIME_absolute_hton(expiration);
-  um->uid = GNUNET_htonll(uid);
-  transmit_for_status (h, cont, cont_cls, timeout);
+  if (cont == NULL)
+    cont = &drop_status_cont;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Asked to update entry %llu raising priority by %u and expiration to %llu\n",
+              uid, (unsigned int) priority,
+              (unsigned long long) expiration.abs_value);
+#endif
+  qc.sc.cont = cont;
+  qc.sc.cont_cls = cont_cls;
+  qe = make_queue_entry (h, sizeof (struct UpdateMessage), queue_priority,
+                         max_queue_size, timeout, &process_status_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry for UPDATE\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop ("# UPDATE requests executed"), 1,
+                            GNUNET_NO);
+  um = (struct UpdateMessage *) &qe[1];
+  um->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_UPDATE);
+  um->header.size = htons (sizeof (struct UpdateMessage));
+  um->priority = htonl (priority);
+  um->expiration = GNUNET_TIME_absolute_hton (expiration);
+  um->uid = GNUNET_htonll (uid);
+  process_queue (h);
+  return qe;
 }
 
 
+/**
+ * Explicitly remove some content from the database.
+ * The "cont"inuation will be called with status
+ * "GNUNET_OK" if content was removed, "GNUNET_NO"
+ * if no matching entry was found and "GNUNET_SYSERR"
+ * on all other types of errors.
+ *
+ * @param h handle to the datastore
+ * @param key key for the value
+ * @param size number of bytes in data
+ * @param data content stored
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response
+ * @param cont continuation to call when done
+ * @param cont_cls closure for cont
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel; note that even if NULL is returned, the callback will be invoked
+ *         (or rather, will already have been invoked)
+ */
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_remove (struct GNUNET_DATASTORE_Handle *h,
+                         const GNUNET_HashCode * key, size_t size,
+                         const void *data, unsigned int queue_priority,
+                         unsigned int max_queue_size,
+                         struct GNUNET_TIME_Relative timeout,
+                         GNUNET_DATASTORE_ContinuationWithStatus cont,
+                         void *cont_cls)
+{
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  struct DataMessage *dm;
+  size_t msize;
+  union QueueContext qc;
+
+  if (cont == NULL)
+    cont = &drop_status_cont;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Asked to remove %u bytes under key `%s'\n", size,
+              GNUNET_h2s (key));
+#endif
+  qc.sc.cont = cont;
+  qc.sc.cont_cls = cont_cls;
+  msize = sizeof (struct DataMessage) + size;
+  GNUNET_assert (msize < GNUNET_SERVER_MAX_MESSAGE_SIZE);
+  qe = make_queue_entry (h, msize, queue_priority, max_queue_size, timeout,
+                         &process_status_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry for REMOVE\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop ("# REMOVE requests executed"), 1,
+                            GNUNET_NO);
+  dm = (struct DataMessage *) &qe[1];
+  dm->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_REMOVE);
+  dm->header.size = htons (msize);
+  dm->rid = htonl (0);
+  dm->size = htonl (size);
+  dm->type = htonl (0);
+  dm->priority = htonl (0);
+  dm->anonymity = htonl (0);
+  dm->uid = GNUNET_htonll (0);
+  dm->expiration = GNUNET_TIME_absolute_hton (GNUNET_TIME_UNIT_ZERO_ABS);
+  dm->key = *key;
+  memcpy (&dm[1], data, size);
+  process_queue (h);
+  return qe;
+}
 
 
 /**
  * Type of a function to call when we receive a message
- * from the service.  This specific function is used
- * to handle messages of type "struct DataMessage".
+ * from the service.
  *
  * @param cls closure
  * @param msg message received, NULL on timeout or fatal error
  */
-static void 
-with_result_response_handler (void *cls,
-			      const struct
-			      GNUNET_MessageHeader * msg)
+static void
+process_result_message (void *cls, const struct GNUNET_MessageHeader *msg)
 {
-  static struct GNUNET_TIME_Absolute zero;
   struct GNUNET_DATASTORE_Handle *h = cls;
-  GNUNET_DATASTORE_Iterator cont = h->response_proc;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  struct ResultContext rc;
   const struct DataMessage *dm;
-  size_t msize;
+  int was_transmitted;
 
   if (msg == NULL)
+  {
+    qe = h->queue_head;
+    GNUNET_assert (NULL != qe);
+    rc = qe->qc.rc;
+    was_transmitted = qe->was_transmitted;
+    free_queue_entry (qe);
+    if (was_transmitted == GNUNET_YES)
     {
-      h->response_proc = NULL;
-      GNUNET_CLIENT_disconnect (h->client);
-      h->client = GNUNET_CLIENT_connect (h->sched, "datastore", h->cfg);
-      cont (h->response_proc_cls, 
-	    NULL, 0, NULL, 0, 0, 0, zero, 0);
-      return;
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  _("Failed to receive response from database.\n"));
+      do_disconnect (h);
     }
-  if (ntohs(msg->type) == GNUNET_MESSAGE_TYPE_DATASTORE_DATA_END) 
+    else
     {
-      GNUNET_break (ntohs(msg->size) == sizeof(struct GNUNET_MessageHeader));
-      h->response_proc = NULL;
+      process_queue (h);
+    }
+    if (rc.proc != NULL)
+      rc.proc (rc.proc_cls, NULL, 0, NULL, 0, 0, 0, GNUNET_TIME_UNIT_ZERO_ABS,
+               0);
+    return;
+  }
+  if (ntohs (msg->type) == GNUNET_MESSAGE_TYPE_DATASTORE_DATA_END)
+  {
+    GNUNET_break (ntohs (msg->size) == sizeof (struct GNUNET_MessageHeader));
+    qe = h->queue_head;
+    rc = qe->qc.rc;
+    GNUNET_assert (GNUNET_YES == qe->was_transmitted);
+    free_queue_entry (qe);
 #if DEBUG_DATASTORE
-      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-		  "Received end of result set\n");
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Received end of result set, new queue size is %u\n",
+                h->queue_size);
 #endif
-      cont (h->response_proc_cls, 
-	    NULL, 0, NULL, 0, 0, 0, zero, 0);
-      return;
-    }
-  if ( (ntohs(msg->size) < sizeof(struct DataMessage)) ||
-       (ntohs(msg->type) != GNUNET_MESSAGE_TYPE_DATASTORE_DATA) ) 
-    {
-      GNUNET_break (0);
-      GNUNET_CLIENT_disconnect (h->client);
-      h->client = GNUNET_CLIENT_connect (h->sched, "datastore", h->cfg);
-      h->response_proc = NULL;
-      cont (h->response_proc_cls, 
-	    NULL, 0, NULL, 0, 0, 0, zero, 0);
-      return;
-    }
-  dm = (const struct DataMessage*) msg;
-  msize = ntohl(dm->size);
-  if (ntohs(msg->size) != msize + sizeof(struct DataMessage))
-    {
-      GNUNET_break (0);
-      GNUNET_CLIENT_disconnect (h->client);
-      h->client = GNUNET_CLIENT_connect (h->sched, "datastore", h->cfg);
-      h->response_proc = NULL;
-      cont (h->response_proc_cls, 
-	    NULL, 0, NULL, 0, 0, 0, zero, 0);
-      return;
-    }
+    if (rc.proc != NULL)
+      rc.proc (rc.proc_cls, NULL, 0, NULL, 0, 0, 0, GNUNET_TIME_UNIT_ZERO_ABS,
+               0);
+    h->retry_time.rel_value = 0;
+    h->result_count = 0;
+    process_queue (h);
+    return;
+  }
+  qe = h->queue_head;
+  GNUNET_assert (NULL != qe);
+  rc = qe->qc.rc;
+  if (GNUNET_YES != qe->was_transmitted)
+  {
+    GNUNET_break (0);
+    free_queue_entry (qe);
+    h->retry_time = GNUNET_TIME_UNIT_ZERO;
+    do_disconnect (h);
+    if (rc.proc != NULL)
+      rc.proc (rc.proc_cls, NULL, 0, NULL, 0, 0, 0, GNUNET_TIME_UNIT_ZERO_ABS,
+               0);
+    return;
+  }
+  if ((ntohs (msg->size) < sizeof (struct DataMessage)) ||
+      (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_DATASTORE_DATA) ||
+      (ntohs (msg->size) !=
+       sizeof (struct DataMessage) +
+       ntohl (((const struct DataMessage *) msg)->size)))
+  {
+    GNUNET_break (0);
+    free_queue_entry (qe);
+    h->retry_time = GNUNET_TIME_UNIT_ZERO;
+    do_disconnect (h);
+    if (rc.proc != NULL)
+      rc.proc (rc.proc_cls, NULL, 0, NULL, 0, 0, 0, GNUNET_TIME_UNIT_ZERO_ABS,
+               0);
+    return;
+  }
+  GNUNET_STATISTICS_update (h->stats, gettext_noop ("# Results received"), 1,
+                            GNUNET_NO);
+  dm = (const struct DataMessage *) msg;
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Received result %llu with type %u and size %u with key %s\n",
-	      (unsigned long long) GNUNET_ntohll(dm->uid),
-	      ntohl(dm->type),
-	      msize,
-	      GNUNET_h2s(&dm->key));
-#endif
-  cont (h->response_proc_cls, 
-	&dm->key,
-	msize,
-	&dm[1],
-	ntohl(dm->type),
-	ntohl(dm->priority),
-	ntohl(dm->anonymity),
-	GNUNET_TIME_absolute_ntoh(dm->expiration),	
-	GNUNET_ntohll(dm->uid));
-  GNUNET_CLIENT_receive (h->client,
-			 &with_result_response_handler,
-			 h,
-			 GNUNET_TIME_absolute_get_remaining (h->timeout));
+              "Received result %llu with type %u and size %u with key %s\n",
+              (unsigned long long) GNUNET_ntohll (dm->uid), ntohl (dm->type),
+              ntohl (dm->size), GNUNET_h2s (&dm->key));
+#endif
+  free_queue_entry (qe);
+  h->retry_time.rel_value = 0;
+  process_queue (h);
+  if (rc.proc != NULL)
+    rc.proc (rc.proc_cls, &dm->key, ntohl (dm->size), &dm[1], ntohl (dm->type),
+             ntohl (dm->priority), ntohl (dm->anonymity),
+             GNUNET_TIME_absolute_ntoh (dm->expiration),
+             GNUNET_ntohll (dm->uid));
 }
 
 
 /**
- * Transmit message to datastore service and then
- * read a result message.
+ * Get a random value from the datastore for content replication.
+ * Returns a single, random value among those with the highest
+ * replication score, lowering positive replication scores by one for
+ * the chosen value (if only content with a replication score exists,
+ * a random value is returned and replication scores are not changed).
  *
- * @param cls closure with handle to datastore
- * @param size number of bytes we can transmit at most
- * @param buf where to write transmission, NULL on
- *        timeout
- * @return number of bytes copied to buf
+ * @param h handle to the datastore
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response
+ * @param proc function to call on a random value; it
+ *        will be called once with a value (if available)
+ *        and always once with a value of NULL.
+ * @param proc_cls closure for proc
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel
  */
-static size_t
-transmit_get_result (void *cls,
-		     size_t size,
-		     void *buf)
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_get_for_replication (struct GNUNET_DATASTORE_Handle *h,
+                                      unsigned int queue_priority,
+                                      unsigned int max_queue_size,
+                                      struct GNUNET_TIME_Relative timeout,
+                                      GNUNET_DATASTORE_DatumProcessor proc,
+                                      void *proc_cls)
 {
-  struct GNUNET_DATASTORE_Handle *h = cls;
-  GNUNET_DATASTORE_ContinuationWithStatus cont = h->response_proc;
-  uint16_t msize;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  struct GNUNET_MessageHeader *m;
+  union QueueContext qc;
 
-  if (buf == NULL)
-    {
-      h->response_proc = NULL;
-      h->message_size = 0;
-      cont (h->response_proc_cls, 
-	    GNUNET_SYSERR,
-	    gettext_noop ("Error transmitting message to datastore service.\n"));
-      return 0;
-    }
-  msize = h->message_size;
-  GNUNET_assert (msize <= size);
-  memcpy (buf, &h[1], msize);
+  GNUNET_assert (NULL != proc);
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Transmitted %u byte message to datastore service, now waiting for result.\n",
-	      msize);
-#endif
-  h->message_size = 0;
-  GNUNET_CLIENT_receive (h->client,
-			 &with_result_response_handler,
-			 h,
-			 GNUNET_TIME_absolute_get_remaining (h->timeout));
-  return msize;
+              "Asked to get replication entry in %llu ms\n",
+              (unsigned long long) timeout.rel_value);
+#endif
+  qc.rc.proc = proc;
+  qc.rc.proc_cls = proc_cls;
+  qe = make_queue_entry (h, sizeof (struct GNUNET_MessageHeader),
+                         queue_priority, max_queue_size, timeout,
+                         &process_result_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry for GET REPLICATION\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop
+                            ("# GET REPLICATION requests executed"), 1,
+                            GNUNET_NO);
+  m = (struct GNUNET_MessageHeader *) &qe[1];
+  m->type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_GET_REPLICATION);
+  m->size = htons (sizeof (struct GNUNET_MessageHeader));
+  process_queue (h);
+  return qe;
 }
 
 
 /**
- * Helper function that will initiate the
- * transmission of a message to the datastore
- * service.  The message must already be prepared
- * and stored in the buffer at the end of the
- * handle.  The message must be of a type that
- * expects a "DataMessage" in response.
+ * Get a single zero-anonymity value from the datastore.
  *
- * @param h handle to the service with prepared message
- * @param cont function to call with result
- * @param cont_cls closure
- * @param timeout timeout for the operation
+ * @param h handle to the datastore
+ * @param offset offset of the result (modulo num-results); set to
+ *               a random 64-bit value initially; then increment by
+ *               one each time; detect that all results have been found by uid
+ *               being again the first uid ever returned.
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
+ * @param timeout how long to wait at most for a response
+ * @param type allowed type for the operation (never zero)
+ * @param proc function to call on a random value; it
+ *        will be called once with a value (if available)
+ *        or with NULL if none value exists.
+ * @param proc_cls closure for proc
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel
  */
-static void
-transmit_for_result (struct GNUNET_DATASTORE_Handle *h,
-		     GNUNET_DATASTORE_Iterator cont,
-		     void *cont_cls,
-		     struct GNUNET_TIME_Relative timeout)
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_get_zero_anonymity (struct GNUNET_DATASTORE_Handle *h,
+                                     uint64_t offset,
+                                     unsigned int queue_priority,
+                                     unsigned int max_queue_size,
+                                     struct GNUNET_TIME_Relative timeout,
+                                     enum GNUNET_BLOCK_Type type,
+                                     GNUNET_DATASTORE_DatumProcessor proc,
+                                     void *proc_cls)
 {
-  static struct GNUNET_TIME_Absolute zero;
-  const struct GNUNET_MessageHeader *hdr;
-  uint16_t msize;
+  struct GNUNET_DATASTORE_QueueEntry *qe;
+  struct GetZeroAnonymityMessage *m;
+  union QueueContext qc;
 
-  GNUNET_assert (cont != NULL);
-  hdr = (const struct GNUNET_MessageHeader*) &h[1];
-  msize = ntohs(hdr->size);
+  GNUNET_assert (NULL != proc);
+  GNUNET_assert (type != GNUNET_BLOCK_TYPE_ANY);
 #if DEBUG_DATASTORE
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-	      "Transmitting %u byte message of type %u to datastore service\n",
-	      msize,
-	      ntohs(hdr->type));
-#endif
-  GNUNET_assert (h->response_proc == NULL);
-  h->response_proc = cont;
-  h->response_proc_cls = cont_cls;
-  h->timeout = GNUNET_TIME_relative_to_absolute (timeout);
-  h->message_size = msize;
-  if (NULL == GNUNET_CLIENT_notify_transmit_ready (h->client,
-						   msize,
-						   timeout,
-						   &transmit_get_result,
-						   h))
-    {
-      GNUNET_break (0);
-      h->response_proc = NULL;
-      h->message_size = 0;
-      cont (h->response_proc_cls, 
-	    NULL, 0, NULL, 0, 0, 0, zero, 0);
-    }
+              "Asked to get %llu-th zero-anonymity entry of type %d in %llu ms\n",
+              (unsigned long long) offset, type,
+              (unsigned long long) timeout.rel_value);
+#endif
+  qc.rc.proc = proc;
+  qc.rc.proc_cls = proc_cls;
+  qe = make_queue_entry (h, sizeof (struct GetZeroAnonymityMessage),
+                         queue_priority, max_queue_size, timeout,
+                         &process_result_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Could not create queue entry for zero-anonymity procation\n");
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats,
+                            gettext_noop
+                            ("# GET ZERO ANONYMITY requests executed"), 1,
+                            GNUNET_NO);
+  m = (struct GetZeroAnonymityMessage *) &qe[1];
+  m->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_GET_ZERO_ANONYMITY);
+  m->header.size = htons (sizeof (struct GetZeroAnonymityMessage));
+  m->type = htonl ((uint32_t) type);
+  m->offset = GNUNET_htonll (offset);
+  process_queue (h);
+  return qe;
 }
 
 
 /**
- * Iterate over the results for a particular key
- * in the datastore.
+ * Get a result for a particular key from the datastore.  The processor
+ * will only be called once.
  *
  * @param h handle to the datastore
+ * @param offset offset of the result (modulo num-results); set to
+ *               a random 64-bit value initially; then increment by
+ *               one each time; detect that all results have been found by uid
+ *               being again the first uid ever returned.
  * @param key maybe NULL (to match all entries)
  * @param type desired type, 0 for any
- * @param iter function to call on each matching value;
- *        will be called once with a NULL value at the end
- * @param iter_cls closure for iter
+ * @param queue_priority ranking of this request in the priority queue
+ * @param max_queue_size at what queue size should this request be dropped
+ *        (if other requests of higher priority are in the queue)
  * @param timeout how long to wait at most for a response
+ * @param proc function to call on each matching value;
+ *        will be called once with a NULL value at the end
+ * @param proc_cls closure for proc
+ * @return NULL if the entry was not queued, otherwise a handle that can be used to
+ *         cancel
  */
-void
-GNUNET_DATASTORE_get (struct GNUNET_DATASTORE_Handle *h,
-                      const GNUNET_HashCode * key,
-                      uint32_t type,
-                      GNUNET_DATASTORE_Iterator iter, void *iter_cls,
-		      struct GNUNET_TIME_Relative timeout)
+struct GNUNET_DATASTORE_QueueEntry *
+GNUNET_DATASTORE_get_key (struct GNUNET_DATASTORE_Handle *h, uint64_t offset,
+                          const GNUNET_HashCode * key,
+                          enum GNUNET_BLOCK_Type type,
+                          unsigned int queue_priority,
+                          unsigned int max_queue_size,
+                          struct GNUNET_TIME_Relative timeout,
+                          GNUNET_DATASTORE_DatumProcessor proc, void *proc_cls)
 {
+  struct GNUNET_DATASTORE_QueueEntry *qe;
   struct GetMessage *gm;
+  union QueueContext qc;
 
-  gm = (struct GetMessage*) &h[1];
-  gm->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_GET);
-  gm->type = htonl(type);
+  GNUNET_assert (NULL != proc);
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Asked to look for data of type %u under key `%s'\n",
+              (unsigned int) type, GNUNET_h2s (key));
+#endif
+  qc.rc.proc = proc;
+  qc.rc.proc_cls = proc_cls;
+  qe = make_queue_entry (h, sizeof (struct GetMessage), queue_priority,
+                         max_queue_size, timeout, &process_result_message, &qc);
+  if (qe == NULL)
+  {
+#if DEBUG_DATASTORE
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Could not queue request for `%s'\n",
+                GNUNET_h2s (key));
+#endif
+    return NULL;
+  }
+  GNUNET_STATISTICS_update (h->stats, gettext_noop ("# GET requests executed"),
+                            1, GNUNET_NO);
+  gm = (struct GetMessage *) &qe[1];
+  gm->header.type = htons (GNUNET_MESSAGE_TYPE_DATASTORE_GET);
+  gm->type = htonl (type);
+  gm->offset = GNUNET_htonll (offset);
   if (key != NULL)
-    {
-      gm->header.size = htons(sizeof (struct GetMessage));
-      gm->key = *key;
-    }
+  {
+    gm->header.size = htons (sizeof (struct GetMessage));
+    gm->key = *key;
+  }
   else
-    {
-      gm->header.size = htons(sizeof (struct GetMessage) - sizeof(GNUNET_HashCode));
-    }
-  transmit_for_result (h, iter, iter_cls, timeout);
-}
-
-
-/**
- * Get a random value from the datastore.
- *
- * @param h handle to the datastore
- * @param iter function to call on a random value; it
- *        will be called exactly once; if no values
- *        are available, the value will be NULL.
- * @param iter_cls closure for iter
- * @param timeout how long to wait at most for a response
- */
-void
-GNUNET_DATASTORE_get_random (struct GNUNET_DATASTORE_Handle *h,
-                             GNUNET_DATASTORE_Iterator iter, void *iter_cls,
-			     struct GNUNET_TIME_Relative timeout)
-{
-  struct GNUNET_MessageHeader *m;
-
-  m = (struct GNUNET_MessageHeader*) &h[1];
-  m->type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_GET_RANDOM);
-  m->size = htons(sizeof (struct GNUNET_MessageHeader));
-  transmit_for_result (h, iter, iter_cls, timeout);
+  {
+    gm->header.size =
+        htons (sizeof (struct GetMessage) - sizeof (GNUNET_HashCode));
+  }
+  process_queue (h);
+  return qe;
 }
 
 
 /**
- * Explicitly remove some content from the database.
- *
- * @param h handle to the datastore
- * @param key key for the value
- * @param size number of bytes in data
- * @param data content stored
- * @param cont continuation to call when done
- * @param cont_cls closure for cont
- * @param timeout how long to wait at most for a response
+ * Cancel a datastore operation.  The final callback from the
+ * operation must not have been done yet.
+ * 
+ * @param qe operation to cancel
  */
 void
-GNUNET_DATASTORE_remove (struct GNUNET_DATASTORE_Handle *h,
-                         const GNUNET_HashCode * key,
-                         uint32_t size, const void *data,
-			 GNUNET_DATASTORE_ContinuationWithStatus cont,
-			 void *cont_cls,
-			 struct GNUNET_TIME_Relative timeout)
+GNUNET_DATASTORE_cancel (struct GNUNET_DATASTORE_QueueEntry *qe)
 {
-  struct DataMessage *dm;
-  size_t msize;
+  struct GNUNET_DATASTORE_Handle *h;
 
-  msize = sizeof(struct DataMessage) + size;
-  GNUNET_assert (msize <= GNUNET_SERVER_MAX_MESSAGE_SIZE);
-  dm = (struct DataMessage*) &h[1];
-  dm->header.type = htons(GNUNET_MESSAGE_TYPE_DATASTORE_REMOVE);
-  dm->header.size = htons(msize);
-  dm->rid = htonl(0);
-  dm->size = htonl(size);
-  dm->type = htonl(0);
-  dm->priority = htonl(0);
-  dm->anonymity = htonl(0);
-  dm->uid = GNUNET_htonll(0);
-  dm->expiration.value = 0;
-  dm->key = *key;
-  memcpy (&dm[1], data, size);
-  transmit_for_status (h, cont, cont_cls, timeout);
+  GNUNET_assert (GNUNET_SYSERR != qe->was_transmitted);
+  h = qe->h;
+#if DEBUG_DATASTORE
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Pending DATASTORE request %p cancelled (%d, %d)\n", qe,
+              qe->was_transmitted, h->queue_head == qe);
+#endif
+  if (GNUNET_YES == qe->was_transmitted)
+  {
+    free_queue_entry (qe);
+    h->skip_next_messages++;
+    return;
+  }
+  free_queue_entry (qe);
+  process_queue (h);
 }