Improve performance of OverrideSearchPathMatchesCurrent().

This function was initially coded on the assumption that it would not be
performance-critical, but that turns out to be wrong in workloads that
are heavily dependent on the speed of plpgsql functions.  Speed it up by
hard-coding the comparison rules, thereby avoiding palloc/pfree traffic
from creating and immediately freeing an OverrideSearchPath object.
Per report from Scott Marlowe.

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 911f015f27ec933c4082660364d672170b86de8e..7a063329fe11fe20f75abe832695274e26d0530e 100644 (file)
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -3145,20 +3145,44 @@ CopyOverrideSearchPath(OverrideSearchPath *path)
 bool
 OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
 {
-   /* Easiest way to do this is GetOverrideSearchPath() and compare */
-   bool        result;
-   OverrideSearchPath *cur;
+   ListCell   *lc,
+              *lcp;
 
-   cur = GetOverrideSearchPath(CurrentMemoryContext);
-   if (path->addCatalog == cur->addCatalog &&
-       path->addTemp == cur->addTemp &&
-       equal(path->schemas, cur->schemas))
-       result = true;
-   else
-       result = false;
-   list_free(cur->schemas);
-   pfree(cur);
-   return result;
+   recomputeNamespacePath();
+
+   /* We scan down the activeSearchPath to see if it matches the input. */
+   lc = list_head(activeSearchPath);
+
+   /* If path->addTemp, first item should be my temp namespace. */
+   if (path->addTemp)
+   {
+       if (lc && lfirst_oid(lc) == myTempNamespace)
+           lc = lnext(lc);
+       else
+           return false;
+   }
+   /* If path->addCatalog, next item should be pg_catalog. */
+   if (path->addCatalog)
+   {
+       if (lc && lfirst_oid(lc) == PG_CATALOG_NAMESPACE)
+           lc = lnext(lc);
+       else
+           return false;
+   }
+   /* We should now be looking at the activeCreationNamespace. */
+   if (activeCreationNamespace != (lc ? lfirst_oid(lc) : InvalidOid))
+       return false;
+   /* The remainder of activeSearchPath should match path->schemas. */
+   foreach(lcp, path->schemas)
+   {
+       if (lc && lfirst_oid(lc) == lfirst_oid(lcp))
+           lc = lnext(lc);
+       else
+           return false;
+   }
+   if (lc)
+       return false;
+   return true;
 }
 
 /*