support older PostGreSQL versions (#4999)

* support older PostGreSQL versions
* documentation accuracy

* improve performance by affecting less rows in UPDATE queries

diff --git a/README.txt b/README.txt
index 8bd8554edbaee8d3e04376cf020514cc509e1af7..4c02763ca93a2d92d82af6f4a6aab0a8f97490ef 100644 (file)
--- a/README.txt
+++ b/README.txt
@@ -178,7 +178,7 @@ ENABLE_FREETYPE     - Build with FreeType2; Allows using TTF fonts
 ENABLE_GETTEXT      - Build with Gettext; Allows using translations
 ENABLE_GLES         - Search for Open GLES headers & libraries and use them
 ENABLE_LEVELDB      - Build with LevelDB; Enables use of LevelDB map backend
-ENABLE_POSTGRESQL   - Build with libpq; Enables use of PostgreSQL map backend (PostgreSQL 9.5 or greater required)
+ENABLE_POSTGRESQL   - Build with libpq; Enables use of PostgreSQL map backend (PostgreSQL 9.5 or greater recommended)
 ENABLE_REDIS        - Build with libhiredis; Enables use of Redis map backend
 ENABLE_SPATIAL      - Build with LibSpatial; Speeds up AreaStores
 ENABLE_SOUND        - Build with OpenAL, libogg & libvorbis; in-game Sounds

diff --git a/src/database-postgresql.cpp b/src/database-postgresql.cpp
index 3b6b42aeac22c81cbec9fdb0c676de0e6b18e680..03a69566bfb5c9c3e789937d5eb92567db2367eb 100644 (file)
--- a/src/database-postgresql.cpp
+++ b/src/database-postgresql.cpp
@@ -80,12 +80,12 @@ void Database_PostgreSQL::connectToDatabase()
 
        /*
        * We are using UPSERT feature from PostgreSQL 9.5
-       * to have the better performance,
-       * set the minimum version to 90500
+       * to have the better performance where possible.
        */
        if (m_pgversion < 90500) {
-               throw DatabaseException("PostgreSQL database error: "
-                       "Server version 9.5 or greater required.");
+               warningstream << "Your PostgreSQL server lacks UPSERT "
+                       << "support. Use version 9.5 or better if possible."
+                       << std::endl;
        }
 
        infostream << "PostgreSQL Database: Version " << m_pgversion
@@ -125,11 +125,25 @@ void Database_PostgreSQL::initStatements()
                        "WHERE posX = $1::int4 AND posY = $2::int4 AND "
                        "posZ = $3::int4");
 
-       prepareStatement("write_block",
+       if (m_pgversion < 90500) {
+               prepareStatement("write_block_insert",
+                       "INSERT INTO blocks (posX, posY, posZ, data) SELECT "
+                       "$1::int4, $2::int4, $3::int4, $4::bytea "
+                       "WHERE NOT EXISTS (SELECT true FROM blocks "
+                       "WHERE posX = $1::int4 AND posY = $2::int4 AND "
+                       "posZ = $3::int4)");
+
+               prepareStatement("write_block_update",
+                       "UPDATE blocks SET data = $4::bytea "
+                       "WHERE posX = $1::int4 AND posY = $2::int4 AND "
+                       "posZ = $3::int4");
+       } else {
+               prepareStatement("write_block",
                        "INSERT INTO blocks (posX, posY, posZ, data) VALUES "
                        "($1::int4, $2::int4, $3::int4, $4::bytea) "
                        "ON CONFLICT ON CONSTRAINT blocks_pkey DO "
                        "UPDATE SET data = $4::bytea");
+       }
 
        prepareStatement("delete_block", "DELETE FROM blocks WHERE "
                        "posX = $1::int4 AND posY = $2::int4 AND posZ = $3::int4");
@@ -218,7 +232,12 @@ bool Database_PostgreSQL::saveBlock(const v3s16 &pos,
        };
        const int argFmt[] = { 1, 1, 1, 1 };
 
-       execPrepared("write_block", ARRLEN(args), args, argLen, argFmt);
+       if (m_pgversion < 90500) {
+               execPrepared("write_block_update", ARRLEN(args), args, argLen, argFmt);
+               execPrepared("write_block_insert", ARRLEN(args), args, argLen, argFmt);
+       } else {
+               execPrepared("write_block", ARRLEN(args), args, argLen, argFmt);
+       }
        return true;
 }