[Tcl-tdbc] tdbc::postgres ConnectionColumnsMethod is slow

[Greg W. <wo...@ee...>]

Hello.  I'm using tdbc::postgres with a fairly large database (PostgreSQL
version 8.4), and while everything is working, I've noticed that issuing
the "columns" command on a large table (~300,000 rows) takes nearly
3 seconds.

The code is executing a "SELECT * FROM table" query, but only retrieving
a single row.  Unfortunately, with my tables, there seems to be a
substantial delay before that row can be retrieved.  I believe that
adding "LIMIT 1" tells the query planner to use a more appropriate plan
for this case.


--- generic/tdbcpostgres.c.bak	2013-05-07 15:08:24.000000000 -0400
+++ generic/tdbcpostgres.c	2013-05-07 14:56:50.000000000 -0400
@@ -1479,6 +1479,7 @@
     /* Check if table exists by retreiving one row.
      * The result wille be later used to determine column types (oids) */
     Tcl_AppendObjToObj(sqlQuery, objv[2]);
+    Tcl_AppendToObj(sqlQuery," LIMIT 1", -1);
 
     if (ExecSimpleQuery(interp, cdata->pgPtr, Tcl_GetString(sqlQuery),
 			&resType) != TCL_OK) {


I've tested this patch, briefly, but not in production yet.  The columns
command definitely runs more quickly.  Does this seem like an appropriate
solution, or have I overlooked something?