1 files changed, 88 insertions, 10 deletions

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 5ff78248e0..2ec23016fe 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -126,6 +126,11 @@
  * namespaceUser is the userid the path has been computed for.
  *
  * Note: all data pointed to by these List variables is in TopMemoryContext.
+ *
+ * activePathGeneration is incremented whenever the effective values of
+ * activeSearchPath/activeCreationNamespace/activeTempCreationPending change.
+ * This can be used to quickly detect whether any change has happened since
+ * a previous examination of the search path state.
  */
 
 /* These variables define the actually active state: */
@@ -138,6 +143,9 @@ static Oid	activeCreationNamespace = InvalidOid;
 /* if true, activeCreationNamespace is wrong, it should be temp namespace */
 static bool activeTempCreationPending = false;
 
+/* current generation counter; make sure this is never zero */
+static uint64 activePathGeneration = 1;
+
 /* These variables are the values last derived from namespace_search_path: */
 
 static List *baseSearchPath = NIL;
@@ -3373,6 +3381,7 @@ GetOverrideSearchPath(MemoryContext context)
 		schemas = list_delete_first(schemas);
 	}
 	result->schemas = schemas;
+	result->generation = activePathGeneration;
 
 	MemoryContextSwitchTo(oldcxt);
 
@@ -3393,12 +3402,18 @@ CopyOverrideSearchPath(OverrideSearchPath *path)
 	result->schemas = list_copy(path->schemas);
 	result->addCatalog = path->addCatalog;
 	result->addTemp = path->addTemp;
+	result->generation = path->generation;
 
 	return result;
 }
 
 /*
  * OverrideSearchPathMatchesCurrent - does path match current setting?
+ *
+ * This is tested over and over in some common code paths, and in the typical
+ * scenario where the active search path seldom changes, it'll always succeed.
+ * We make that case fast by keeping a generation counter that is advanced
+ * whenever the active search path changes.
  */
 bool
 OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
@@ -3408,6 +3423,10 @@ OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
 
 	recomputeNamespacePath();
 
+	/* Quick out if already known equal to active path. */
+	if (path->generation == activePathGeneration)
+		return true;
+
 	/* We scan down the activeSearchPath to see if it matches the input. */
 	lc = list_head(activeSearchPath);
 
@@ -3440,6 +3459,13 @@ OverrideSearchPathMatchesCurrent(OverrideSearchPath *path)
 	}
 	if (lc)
 		return false;
+
+	/*
+	 * Update path->generation so that future tests will return quickly, so
+	 * long as the active search path doesn't change.
+	 */
+	path->generation = activePathGeneration;
+
 	return true;
 }
 
@@ -3510,6 +3536,14 @@ PushOverrideSearchPath(OverrideSearchPath *newpath)
 	activeCreationNamespace = entry->creationNamespace;
 	activeTempCreationPending = false;	/* XXX is this OK? */
 
+	/*
+	 * We always increment activePathGeneration when pushing/popping an
+	 * override path.  In current usage, these actions always change the
+	 * effective path state, so there's no value in checking to see if it
+	 * didn't change.
+	 */
+	activePathGeneration++;
+
 	MemoryContextSwitchTo(oldcxt);
 }
 
@@ -3551,6 +3585,9 @@ PopOverrideSearchPath(void)
 		activeCreationNamespace = baseCreationNamespace;
 		activeTempCreationPending = baseTempCreationPending;
 	}
+
+	/* As above, the generation always increments. */
+	activePathGeneration++;
 }
 
 
@@ -3707,6 +3744,7 @@ recomputeNamespacePath(void)
 	ListCell   *l;
 	bool		temp_missing;
 	Oid			firstNS;
+	bool		pathChanged;
 	MemoryContext oldcxt;
 
 	/* Do nothing if an override search spec is active. */
@@ -3814,18 +3852,31 @@ recomputeNamespacePath(void)
 		oidlist = lcons_oid(myTempNamespace, oidlist);
 
 	/*
-	 * Now that we've successfully built the new list of namespace OIDs, save
-	 * it in permanent storage.
+	 * We want to detect the case where the effective value of the base search
+	 * path variables didn't change.  As long as we're doing so, we can avoid
+	 * copying the OID list unncessarily.
 	 */
-	oldcxt = MemoryContextSwitchTo(TopMemoryContext);
-	newpath = list_copy(oidlist);
-	MemoryContextSwitchTo(oldcxt);
+	if (baseCreationNamespace == firstNS &&
+		baseTempCreationPending == temp_missing &&
+		equal(oidlist, baseSearchPath))
+	{
+		pathChanged = false;
+	}
+	else
+	{
+		pathChanged = true;
+
+		/* Must save OID list in permanent storage. */
+		oldcxt = MemoryContextSwitchTo(TopMemoryContext);
+		newpath = list_copy(oidlist);
+		MemoryContextSwitchTo(oldcxt);
 
-	/* Now safe to assign to state variables. */
-	list_free(baseSearchPath);
-	baseSearchPath = newpath;
-	baseCreationNamespace = firstNS;
-	baseTempCreationPending = temp_missing;
+		/* Now safe to assign to state variables. */
+		list_free(baseSearchPath);
+		baseSearchPath = newpath;
+		baseCreationNamespace = firstNS;
+		baseTempCreationPending = temp_missing;
+	}
 
 	/* Mark the path valid. */
 	baseSearchPathValid = true;
@@ -3836,6 +3887,16 @@ recomputeNamespacePath(void)
 	activeCreationNamespace = baseCreationNamespace;
 	activeTempCreationPending = baseTempCreationPending;
 
+	/*
+	 * Bump the generation only if something actually changed.  (Notice that
+	 * what we compared to was the old state of the base path variables; so
+	 * this does not deal with the situation where we have just popped an
+	 * override path and restored the prior state of the base path.  Instead
+	 * we rely on the override-popping logic to have bumped the generation.)
+	 */
+	if (pathChanged)
+		activePathGeneration++;
+
 	/* Clean up. */
 	pfree(rawname);
 	list_free(namelist);
@@ -4054,6 +4115,8 @@ AtEOXact_Namespace(bool isCommit, bool parallel)
 		activeSearchPath = baseSearchPath;
 		activeCreationNamespace = baseCreationNamespace;
 		activeTempCreationPending = baseTempCreationPending;
+		/* Always bump generation --- see note in recomputeNamespacePath */
+		activePathGeneration++;
 	}
 }
 
@@ -4109,6 +4172,8 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 		overrideStack = list_delete_first(overrideStack);
 		list_free(entry->searchPath);
 		pfree(entry);
+		/* Always bump generation --- see note in recomputeNamespacePath */
+		activePathGeneration++;
 	}
 
 	/* Activate the next level down. */
@@ -4118,6 +4183,12 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 		activeSearchPath = entry->searchPath;
 		activeCreationNamespace = entry->creationNamespace;
 		activeTempCreationPending = false;	/* XXX is this OK? */
+
+		/*
+		 * It's probably unnecessary to bump generation here, but this should
+		 * not be a performance-critical case, so better to be over-cautious.
+		 */
+		activePathGeneration++;
 	}
 	else
 	{
@@ -4125,6 +4196,12 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 		activeSearchPath = baseSearchPath;
 		activeCreationNamespace = baseCreationNamespace;
 		activeTempCreationPending = baseTempCreationPending;
+
+		/*
+		 * If we popped an override stack entry, then we already bumped the
+		 * generation above.  If we did not, then the above assignments did
+		 * nothing and we need not bump the generation.
+		 */
 	}
 }
 
@@ -4264,6 +4341,7 @@ InitializeSearchPath(void)
 		activeSearchPath = baseSearchPath;
 		activeCreationNamespace = baseCreationNamespace;
 		activeTempCreationPending = baseTempCreationPending;
+		activePathGeneration++; /* pro forma */
 	}
 	else
 	{