pgsql: Speed up resync().

lib/modules/Sql.pmod/pgsql.pike

@@ -1170,7 +1170,7 @@ private void startquery(int forcetext, .pgsql_util.Result portal, string q,
       ERROR("Current transaction is aborted, "
        "commands ignored until end of transaction");
   }
-  if (transtype != NOTRANS)
+  if (transtype != NOTRANS || .pgsql_util.nodataresprefix->match(q))
     tp = .pgsql_util.describenodata;		// Description already known
   else if (!forcetext && forcecache == 1
         || forcecache && sizeof(q) >= MINPREPARELENGTH) {

lib/modules/Sql.pmod/pgsql_util.pmod

@@ -110,7 +110,7 @@ private Regexp dontcacheprefix = iregexp("^\a*(FETCH|COPY)\a");
 private Regexp paralleliseprefix
  = iregexp("^\a*((SELEC|INSER)T|(UPDA|DELE)TE|(FETC|WIT)H)\a");
 
- /* Statements matching transbeginprefix will cause the driver
+ /* Statements matching transbeginprefix will cause the driver to
   * insert a sync after the statement.
   * Failure to do so, will result in portal synchronisation errors
   * in the event of an ErrorResponse.
@@ -118,7 +118,7 @@ private Regexp paralleliseprefix
 final Regexp transbeginprefix
  = iregexp("^\a*(BEGIN|START)([; \t\f\r\n]|$)");
 
- /* Statements matching transendprefix will cause the driver
+ /* Statements matching transendprefix will cause the driver to
   * insert a sync after the statement.
   * Failure to do so, will result in portal synchronisation errors
   * in the event of an ErrorResponse.
@@ -126,6 +126,13 @@ final Regexp transbeginprefix
 final Regexp transendprefix
  = iregexp("^\a*(COMMIT|ROLLBACK|END)([; \t\f\r\n]|$)");
 
+ /* Statements matching nodataresprefix will cause the driver
+  * to skip asking for a query description and query results, since there
+  * are no arguments or results to begin with.
+  */
+final Regexp nodataresprefix
+ = iregexp("^\a*(RESET|CLOSE|DISCARD)\a");
+
  /* For statements matching execfetchlimit the resultrows will not be
   * fetched in pieces.  This heuristic will be sub-optimal whenever
   * either an UPDATE/DELETE/INSERT statement is prefixed by WITH, or
@@ -139,7 +146,7 @@ final Regexp transendprefix
   * tradeoff.
   */
 private Regexp execfetchlimit
- = iregexp("^\a*((UPDA|DELE)TE|INSERT"
+ = iregexp("^\a*((UPDA|DELE)TE|INSERT|CREATE|DROP"
            "|RESET|CLOSE|DISCARD)\a|\aLIMIT\a+[1-9][; \t\f\r\n]*$");
 
 private void default_backend_runs() {		// Runs as soon as the