On Tue, 2023-08-01 at 21:52 -0700, Nathan Bossart wrote:
> I
> typically see this done with two ѕeparate lists and forboth().

Agreed, done.

> 
> Any reason not to use hash_combine() here?

Thank you, fixed.

> > I changed it to move the hook so that it's called after retrieving
> > from
> > the cache.
...
> I think you are right.  This adds some complexity, but I don't have
> anything else to propose at the moment.

I reworked it a bit to avoid allocations in most cases, and it only
reprocesses the oidlist and runs the hooks when necessary (and even
then, still benefits from the cached OIDs that have already passed the
ACL checks).

Now I'm seeing timings around 7.1s, which is starting to look really
nice.

> 
> I'm not following why this logic was moved.

There was previously a comment:

    "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 unnecessarily."

But with v2 the copy had already happened by that point. In v3, there
is no copy at all.
> 

Regards,
        Jeff Davis


From d9a3d4364731a152096d4a8c8cf6a81c1e86f8ab Mon Sep 17 00:00:00 2001
From: Jeff Davis <j...@j-davis.com>
Date: Thu, 27 Jul 2023 15:11:42 -0700
Subject: [PATCH v3 1/3] Transform proconfig for faster execution.

Store function config settings as a list of (name, value) pairs to
avoid the need to parse for each function invocation.
---
 src/backend/utils/fmgr/fmgr.c | 29 +++++++++++++++-------
 src/backend/utils/misc/guc.c  | 45 ++++++++++++++++++++++++++++-------
 src/include/utils/guc.h       |  2 ++
 3 files changed, 59 insertions(+), 17 deletions(-)

diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index 9208c31fe0..6b2d7d7be3 100644
--- a/src/backend/utils/fmgr/fmgr.c
+++ b/src/backend/utils/fmgr/fmgr.c
@@ -612,7 +612,8 @@ struct fmgr_security_definer_cache
 {
 	FmgrInfo	flinfo;			/* lookup info for target function */
 	Oid			userid;			/* userid to set, or InvalidOid */
-	ArrayType  *proconfig;		/* GUC values to set, or NULL */
+	List	   *configNames;	/* GUC names to set, or NIL */
+	List	   *configValues;	/* GUC values to set, or NIL */
 	Datum		arg;			/* passthrough argument for plugin modules */
 };
 
@@ -634,6 +635,8 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 	FmgrInfo   *save_flinfo;
 	Oid			save_userid;
 	int			save_sec_context;
+	ListCell   *lc1;
+	ListCell   *lc2;
 	volatile int save_nestlevel;
 	PgStat_FunctionCallUsage fcusage;
 
@@ -666,8 +669,11 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 								&isnull);
 		if (!isnull)
 		{
+			ArrayType *array;
 			oldcxt = MemoryContextSwitchTo(fcinfo->flinfo->fn_mcxt);
-			fcache->proconfig = DatumGetArrayTypePCopy(datum);
+			array = DatumGetArrayTypeP(datum);
+			TransformGUCArray(array, &fcache->configNames,
+							  &fcache->configValues);
 			MemoryContextSwitchTo(oldcxt);
 		}
 
@@ -680,7 +686,7 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 
 	/* GetUserIdAndSecContext is cheap enough that no harm in a wasted call */
 	GetUserIdAndSecContext(&save_userid, &save_sec_context);
-	if (fcache->proconfig)		/* Need a new GUC nesting level */
+	if (fcache->configNames != NIL)		/* Need a new GUC nesting level */
 		save_nestlevel = NewGUCNestLevel();
 	else
 		save_nestlevel = 0;		/* keep compiler quiet */
@@ -689,12 +695,17 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 		SetUserIdAndSecContext(fcache->userid,
 							   save_sec_context | SECURITY_LOCAL_USERID_CHANGE);
 
-	if (fcache->proconfig)
+	forboth(lc1, fcache->configNames, lc2, fcache->configValues)
 	{
-		ProcessGUCArray(fcache->proconfig,
-						(superuser() ? PGC_SUSET : PGC_USERSET),
-						PGC_S_SESSION,
-						GUC_ACTION_SAVE);
+		GucContext	 context = superuser() ? PGC_SUSET : PGC_USERSET;
+		GucSource	 source	 = PGC_S_SESSION;
+		GucAction	 action	 = GUC_ACTION_SAVE;
+		char		*name	 = lfirst(lc1);
+		char		*value	 = lfirst(lc2);
+
+		(void) set_config_option(name, value,
+								 context, source,
+								 action, true, 0, false);
 	}
 
 	/* function manager hook */
@@ -737,7 +748,7 @@ fmgr_security_definer(PG_FUNCTION_ARGS)
 
 	fcinfo->flinfo = save_flinfo;
 
-	if (fcache->proconfig)
+	if (fcache->configNames != NIL)
 		AtEOXact_GUC(true, save_nestlevel);
 	if (OidIsValid(fcache->userid))
 		SetUserIdAndSecContext(save_userid, save_sec_context);
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5308896c87..fa96b79192 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -6213,16 +6213,13 @@ ParseLongOption(const char *string, char **name, char **value)
 			*cp = '_';
 }
 
-
 /*
- * Handle options fetched from pg_db_role_setting.setconfig,
- * pg_proc.proconfig, etc.  Caller must specify proper context/source/action.
- *
- * The array parameter must be an array of TEXT (it must not be NULL).
+ * Transform array of GUC settings into a list of (name, value) pairs. The
+ * list is faster to process in cases where the settings must be applied
+ * repeatedly (e.g. for each function invocation).
  */
 void
-ProcessGUCArray(ArrayType *array,
-				GucContext context, GucSource source, GucAction action)
+TransformGUCArray(ArrayType *array, List **names, List **values)
 {
 	int			i;
 
@@ -6231,6 +6228,8 @@ ProcessGUCArray(ArrayType *array,
 	Assert(ARR_NDIM(array) == 1);
 	Assert(ARR_LBOUND(array)[0] == 1);
 
+	*names = NIL;
+	*values = NIL;
 	for (i = 1; i <= ARR_DIMS(array)[0]; i++)
 	{
 		Datum		d;
@@ -6262,14 +6261,44 @@ ProcessGUCArray(ArrayType *array,
 			continue;
 		}
 
+		*names = lappend(*names, name);
+		*values = lappend(*values, value);
+
+		pfree(s);
+	}
+}
+
+/*
+ * Handle options fetched from pg_db_role_setting.setconfig,
+ * pg_proc.proconfig, etc.  Caller must specify proper context/source/action.
+ *
+ * The array parameter must be an array of TEXT (it must not be NULL).
+ */
+void
+ProcessGUCArray(ArrayType *array,
+				GucContext context, GucSource source, GucAction action)
+{
+	List *gucNames;
+	List *gucValues;
+	ListCell *lc1;
+	ListCell *lc2;
+
+	TransformGUCArray(array, &gucNames, &gucValues);
+	forboth(lc1, gucNames, lc2, gucValues)
+	{
+		char *name = lfirst(lc1);
+		char *value = lfirst(lc2);
+
 		(void) set_config_option(name, value,
 								 context, source,
 								 action, true, 0, false);
 
 		pfree(name);
 		pfree(value);
-		pfree(s);
 	}
+
+	list_free(gucNames);
+	list_free(gucValues);
 }
 
 
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index 223a19f80d..e89083ee0e 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -391,6 +391,8 @@ extern void AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt);
 extern char *GetConfigOptionByName(const char *name, const char **varname,
 								   bool missing_ok);
 
+extern void TransformGUCArray(ArrayType *array, List **configNames,
+							  List **configValues);
 extern void ProcessGUCArray(ArrayType *array,
 							GucContext context, GucSource source, GucAction action);
 extern ArrayType *GUCArrayAdd(ArrayType *array, const char *name, const char *value);
-- 
2.34.1

From c87434fb268a1dea49bf6d085ff47d6c8d22fab5 Mon Sep 17 00:00:00 2001
From: Jeff Davis <j...@j-davis.com>
Date: Thu, 27 Jul 2023 15:23:51 -0700
Subject: [PATCH v3 2/3] Optimize check_search_path().

Introduce CheckIdentifierString(), which validates a string list of
identifiers without the work of actually storing them in a list.

This speeds up frequent search_path changes, such as when a function
has search_path set in proconfig. Based on profiling.
---
 src/backend/catalog/namespace.c | 13 +-----
 src/backend/utils/adt/varlena.c | 70 +++++++++++++++++++++++++++++++++
 src/include/utils/varlena.h     |  1 +
 3 files changed, 73 insertions(+), 11 deletions(-)

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index 1f76b5d7f7..f457f778cb 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -4101,19 +4101,13 @@ ResetTempTableNamespace(void)
 bool
 check_search_path(char **newval, void **extra, GucSource source)
 {
-	char	   *rawname;
-	List	   *namelist;
-
-	/* Need a modifiable copy of string */
-	rawname = pstrdup(*newval);
+	char *rawname = *newval;
 
 	/* Parse string into list of identifiers */
-	if (!SplitIdentifierString(rawname, ',', &namelist))
+	if (!CheckIdentifierString(rawname, ','))
 	{
 		/* syntax error in name list */
 		GUC_check_errdetail("List syntax is invalid.");
-		pfree(rawname);
-		list_free(namelist);
 		return false;
 	}
 
@@ -4125,9 +4119,6 @@ check_search_path(char **newval, void **extra, GucSource source)
 	 * requirement is syntactic validity of the identifier list.
 	 */
 
-	pfree(rawname);
-	list_free(namelist);
-
 	return true;
 }
 
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index b1ec5c32ce..c8d36fd868 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -3427,6 +3427,76 @@ textToQualifiedNameList(text *textval)
 	return result;
 }
 
+/*
+ * Check that an identifier list is syntactically valid; that is, that there
+ * are no mismatched quotes and that identifiers are separated with the given
+ * separator. Empty identifiers are considered acceptable if (and only if)
+ * quoted.
+ *
+ * Note that an empty string is considered okay here, though not in
+ * textToQualifiedNameList.
+ */
+bool
+CheckIdentifierString(const char *rawstring, char separator)
+{
+	const char *nextp = rawstring;
+	bool		done = false;
+
+	while (scanner_isspace(*nextp))
+		nextp++;				/* skip leading whitespace */
+
+	if (*nextp == '\0')
+		return true;			/* allow empty string */
+
+	/* At the top of the loop, we are at start of a new identifier. */
+	do
+	{
+		if (*nextp == '"')
+		{
+			for (;;)
+			{
+				nextp = strchr(nextp + 1, '"');
+				if (nextp == NULL)
+					return false;	/* mismatched quotes */
+				if (nextp[1] != '"')
+					break;		/* found end of quoted name */
+				nextp++;
+			}
+
+			nextp++;
+		}
+		else
+		{
+			/* Unquoted name --- extends to separator or whitespace */
+			const char *curname = nextp;
+			while (*nextp && *nextp != separator &&
+				   !scanner_isspace(*nextp))
+				nextp++;
+			if (curname == nextp)
+				return false;	/* empty unquoted name not allowed */
+		}
+
+		while (scanner_isspace(*nextp))
+			nextp++;			/* skip trailing whitespace */
+
+		if (*nextp == separator)
+		{
+			nextp++;
+			while (scanner_isspace(*nextp))
+				nextp++;		/* skip leading whitespace for next */
+			/* we expect another name, so done remains false */
+		}
+		else if (*nextp == '\0')
+			done = true;
+		else
+			return false;		/* invalid syntax */
+
+		/* Loop back if we didn't reach end of string */
+	} while (!done);
+
+	return true;
+}
+
 /*
  * SplitIdentifierString --- parse a string containing identifiers
  *
diff --git a/src/include/utils/varlena.h b/src/include/utils/varlena.h
index 77f5b24735..4ff0cecc91 100644
--- a/src/include/utils/varlena.h
+++ b/src/include/utils/varlena.h
@@ -27,6 +27,7 @@ extern int	varstr_levenshtein_less_equal(const char *source, int slen,
 										  int ins_c, int del_c, int sub_c,
 										  int max_d, bool trusted);
 extern List *textToQualifiedNameList(text *textval);
+extern bool CheckIdentifierString(const char *rawstring, char separator);
 extern bool SplitIdentifierString(char *rawstring, char separator,
 								  List **namelist);
 extern bool SplitDirectoriesString(char *rawstring, char separator,
-- 
2.34.1

From ee777f9f668330f7578af5b7be331b625a5b1fd8 Mon Sep 17 00:00:00 2001
From: Jeff Davis <j...@j-davis.com>
Date: Wed, 26 Jul 2023 12:55:09 -0700
Subject: [PATCH v3 3/3] Add cache for recomputeNamespacePath().

When search_path is changed to something that was previously set, and
no invalidation happened in between, use the cached list of namespace
OIDs rather than recomputing them. This avoids syscache lookups and
ACL checks.

Important when the search_path changes frequently, such as when set in
proconfig.
---
 src/backend/catalog/namespace.c | 336 ++++++++++++++++++++++++++------
 1 file changed, 273 insertions(+), 63 deletions(-)

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index f457f778cb..58b78f798d 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -41,6 +41,7 @@
 #include "catalog/pg_ts_template.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
+#include "common/hashfn.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
@@ -109,11 +110,12 @@
  * activeSearchPath is always the actually active path; it points to
  * to baseSearchPath which is the list derived from namespace_search_path.
  *
- * If baseSearchPathValid is false, then baseSearchPath (and other
- * derived variables) need to be recomputed from namespace_search_path.
- * We mark it invalid upon an assignment to namespace_search_path or receipt
- * of a syscache invalidation event for pg_namespace.  The recomputation
- * is done during the next lookup attempt.
+ * If baseSearchPathValid is false, then baseSearchPath (and other derived
+ * variables) need to be recomputed from namespace_search_path, or retrieved
+ * from the search path cache if there haven't been any syscache
+ * invalidations.  We mark it invalid upon an assignment to
+ * namespace_search_path or receipt of a syscache invalidation event for
+ * pg_namespace.  The recomputation is done during the next lookup attempt.
  *
  * Any namespaces mentioned in namespace_search_path that are not readable
  * by the current user ID are simply left out of baseSearchPath; so
@@ -153,6 +155,33 @@ static Oid	namespaceUser = InvalidOid;
 
 /* The above four values are valid only if baseSearchPathValid */
 static bool baseSearchPathValid = true;
+static bool searchPathCacheValid = false;
+static MemoryContext SearchPathCacheContext = NULL;
+
+typedef struct SearchPathCacheKey
+{
+	const char	*searchPath;
+	Oid			 roleid;
+} SearchPathCacheKey;
+
+typedef struct SearchPathCacheEntry
+{
+	SearchPathCacheKey	*key;
+	List				*oidlist;	/* namespace OIDs that pass ACL checks */
+	List				*finalPath;	/* cached final computed search path */
+	Oid					 firstNS;	/* first explicitly-listed namespace */
+	bool				 temp_missing;
+
+	/*
+	 * If true, some namespaces were previously filtered out of finalPath by a
+	 * namespace search hook. The next time it's read from the cache, we need
+	 * to recreate finalPath from the oidlist.
+	 */
+	bool				 hook_filtered;
+
+	/* needed for simplehash */
+	char				 status;
+} SearchPathCacheEntry;
 
 /*
  * myTempNamespace is InvalidOid until and unless a TEMP namespace is set up
@@ -193,6 +222,45 @@ static bool MatchNamedCall(HeapTuple proctup, int nargs, List *argnames,
 						   bool include_out_arguments, int pronargs,
 						   int **argnumbers);
 
+/*
+ * Recomputing the namespace path can be costly when done frequently, such as
+ * when a function has search_path set in proconfig. Add a cache that can be
+ * used when the search_path changes to a value that was previously set, and
+ * no invalidation intervened.
+ *
+ * The cache is a simple hash table in its own memory context, with a key of
+ * search_path and role ID.
+ */
+
+static inline uint32
+nspcachekey_hash(SearchPathCacheKey *key)
+{
+	const unsigned char	*bytes = (const unsigned char *)key->searchPath;
+	int					 blen  = strlen(key->searchPath);
+
+	return hash_combine(hash_bytes(bytes, blen),
+						hash_uint32(key->roleid));
+}
+
+static inline bool
+nspcachekey_equal(SearchPathCacheKey *a, SearchPathCacheKey *b)
+{
+	return a->roleid == b->roleid &&
+		strcmp(a->searchPath, b->searchPath) == 0;
+}
+
+#define SH_PREFIX		nsphash
+#define SH_ELEMENT_TYPE	SearchPathCacheEntry
+#define SH_KEY_TYPE		SearchPathCacheKey *
+#define	SH_KEY			key
+#define SH_HASH_KEY(tb, key)   	nspcachekey_hash(key)
+#define SH_EQUAL(tb, a, b)		nspcachekey_equal(a, b)
+#define	SH_SCOPE		static inline
+#define SH_DECLARE
+#define SH_DEFINE
+#include "lib/simplehash.h"
+
+static nsphash_hash *SearchPathCache = NULL;
 
 /*
  * RangeVarGetRelidExtended
@@ -3370,6 +3438,7 @@ SetTempNamespaceState(Oid tempNamespaceId, Oid tempToastNamespaceId)
 	 */
 
 	baseSearchPathValid = false;	/* may need to rebuild list */
+	searchPathCacheValid = false;
 }
 
 
@@ -3633,28 +3702,19 @@ FindDefaultConversionProc(int32 for_encoding, int32 to_encoding)
 }
 
 /*
- * recomputeNamespacePath - recompute path derived variables if needed.
+ * Look up namespace IDs and perform ACL checks. Return newly-allocated list.
  */
-static void
-recomputeNamespacePath(void)
+static List *
+preprocessNamespacePath(const char *searchPath, Oid roleid,
+						bool *temp_missing)
 {
-	Oid			roleid = GetUserId();
 	char	   *rawname;
 	List	   *namelist;
 	List	   *oidlist;
-	List	   *newpath;
 	ListCell   *l;
-	bool		temp_missing;
-	Oid			firstNS;
-	bool		pathChanged;
-	MemoryContext oldcxt;
 
-	/* Do nothing if path is already valid. */
-	if (baseSearchPathValid && namespaceUser == roleid)
-		return;
-
-	/* Need a modifiable copy of namespace_search_path string */
-	rawname = pstrdup(namespace_search_path);
+	/* Need a modifiable copy */
+	rawname = pstrdup(searchPath);
 
 	/* Parse string into list of identifiers */
 	if (!SplitIdentifierString(rawname, ',', &namelist))
@@ -3671,7 +3731,7 @@ recomputeNamespacePath(void)
 	 * already been accepted.)	Don't make duplicate entries, either.
 	 */
 	oidlist = NIL;
-	temp_missing = false;
+	*temp_missing = false;
 	foreach(l, namelist)
 	{
 		char	   *curname = (char *) lfirst(l);
@@ -3691,10 +3751,8 @@ recomputeNamespacePath(void)
 				namespaceId = get_namespace_oid(rname, true);
 				ReleaseSysCache(tuple);
 				if (OidIsValid(namespaceId) &&
-					!list_member_oid(oidlist, namespaceId) &&
 					object_aclcheck(NamespaceRelationId, namespaceId, roleid,
-									ACL_USAGE) == ACLCHECK_OK &&
-					InvokeNamespaceSearchHook(namespaceId, false))
+									ACL_USAGE) == ACLCHECK_OK)
 					oidlist = lappend_oid(oidlist, namespaceId);
 			}
 		}
@@ -3702,16 +3760,12 @@ recomputeNamespacePath(void)
 		{
 			/* pg_temp --- substitute temp namespace, if any */
 			if (OidIsValid(myTempNamespace))
-			{
-				if (!list_member_oid(oidlist, myTempNamespace) &&
-					InvokeNamespaceSearchHook(myTempNamespace, false))
-					oidlist = lappend_oid(oidlist, myTempNamespace);
-			}
+				oidlist = lappend_oid(oidlist, myTempNamespace);
 			else
 			{
 				/* If it ought to be the creation namespace, set flag */
 				if (oidlist == NIL)
-					temp_missing = true;
+					*temp_missing = true;
 			}
 		}
 		else
@@ -3719,63 +3773,207 @@ recomputeNamespacePath(void)
 			/* normal namespace reference */
 			namespaceId = get_namespace_oid(curname, true);
 			if (OidIsValid(namespaceId) &&
-				!list_member_oid(oidlist, namespaceId) &&
 				object_aclcheck(NamespaceRelationId, namespaceId, roleid,
-								ACL_USAGE) == ACLCHECK_OK &&
-				InvokeNamespaceSearchHook(namespaceId, false))
+								ACL_USAGE) == ACLCHECK_OK)
 				oidlist = lappend_oid(oidlist, namespaceId);
 		}
 	}
 
+	pfree(rawname);
+	list_free(namelist);
+
+	return oidlist;
+}
+
+/*
+ * Remove duplicates, run namespace search hooks, and prepend
+ * implicitly-searched namespaces. Return newly-allocated list.
+ *
+ * All of this must happen after retrieving from cache, because we don't know
+ * what might invalidate the result from the last time the hook was
+ * invoked. It may seem that duplicate elimination is not dependent on the
+ * result of the hook, but if a hook returns different results on different
+ * calls for the same namespace ID, then it could affect the order in which
+ * that namespace appears in the final list.
+ */
+static List *
+finalNamespacePath(List *oidlist, Oid *firstNS, bool *hook_filtered)
+{
+	List		*finalPath = NIL;
+	ListCell	*lc;
+
+	*hook_filtered = false;
+	foreach(lc, oidlist)
+	{
+		Oid namespaceId = lfirst_oid(lc);
+		if (!list_member_oid(finalPath, namespaceId))
+		{
+			if (InvokeNamespaceSearchHook(namespaceId, false))
+				finalPath = lappend_oid(finalPath, namespaceId);
+			else
+				*hook_filtered = true;
+		}
+	}
+
 	/*
 	 * Remember the first member of the explicit list.  (Note: this is
 	 * nominally wrong if temp_missing, but we need it anyway to distinguish
 	 * explicit from implicit mention of pg_catalog.)
 	 */
-	if (oidlist == NIL)
-		firstNS = InvalidOid;
+	if (finalPath == NIL)
+		*firstNS = InvalidOid;
 	else
-		firstNS = linitial_oid(oidlist);
+		*firstNS = linitial_oid(finalPath);
 
 	/*
 	 * Add any implicitly-searched namespaces to the list.  Note these go on
 	 * the front, not the back; also notice that we do not check USAGE
 	 * permissions for these.
 	 */
-	if (!list_member_oid(oidlist, PG_CATALOG_NAMESPACE))
-		oidlist = lcons_oid(PG_CATALOG_NAMESPACE, oidlist);
+	if (!list_member_oid(finalPath, PG_CATALOG_NAMESPACE))
+		finalPath = lcons_oid(PG_CATALOG_NAMESPACE, finalPath);
 
 	if (OidIsValid(myTempNamespace) &&
-		!list_member_oid(oidlist, myTempNamespace))
-		oidlist = lcons_oid(myTempNamespace, oidlist);
+		!list_member_oid(finalPath, myTempNamespace))
+		finalPath = lcons_oid(myTempNamespace, finalPath);
+
+	return finalPath;
+}
+
+/*
+ * Retrieve search path information from the cache; or if not present,
+ * recompute it and add it to the cache.
+ *
+ * This function is also able to take the previous path and compare it to the
+ * newly-computed path. We perform the equality check in this function rather
+ * than the caller because this function can often avoid making a temporary
+ * copy of the previous path.
+ *
+ * Return OID list allocated in SearchPathCacheContext. The result is valid
+ * until the next call to this function, which may deallocate previous
+ * results.
+ */
+static List *
+cachedNamespacePath(const char *searchPath, Oid roleid,
+					Oid *firstNS, bool *temp_missing,
+					List *prevPath, bool *prevPathEqual)
+{
+	MemoryContext			 oldcxt;
+	SearchPathCacheKey		 cachekey;
+	SearchPathCacheEntry	*entry;
+	bool					 found;
+	bool					 prevPathFree = false;
+
+	/* clear the cache and start over when invalidated */
+	if (!searchPathCacheValid)
+	{
+		/* temporarily save prevPath for comparison after reset */
+		prevPath = list_copy(prevPath);
+		prevPathFree = true;
+		MemoryContextReset(SearchPathCacheContext);
+
+		/* arbitrary initial starting size of 16 elements */
+		SearchPathCache = nsphash_create(SearchPathCacheContext, 16, NULL);
+		searchPathCacheValid = true;
+	}
+
+	cachekey.searchPath = searchPath;
+	cachekey.roleid = roleid;
+
+	entry = nsphash_insert(SearchPathCache, &cachekey, &found);
+
+	if (!found)
+	{
+		SearchPathCacheKey	*newkey;
+		List				*oidlist;
+
+		oidlist = preprocessNamespacePath(searchPath, roleid,
+										  &entry->temp_missing);
+
+		oldcxt = MemoryContextSwitchTo(SearchPathCacheContext);
+
+		newkey = palloc(sizeof(SearchPathCacheKey));
+		newkey->searchPath = pstrdup(searchPath);
+		newkey->roleid = roleid;
+
+		entry->key = newkey;
+		entry->oidlist = list_copy(oidlist);
+		entry->finalPath = finalNamespacePath(oidlist,
+											  &entry->firstNS,
+											  &entry->hook_filtered);
+		MemoryContextSwitchTo(oldcxt);
+
+		/* oidlist already copied into cache entry */
+		list_free(oidlist);
+	}
+	else
+	{
+		/*
+		 * The namespace search hook doesn't invalidate the cache, so if a
+		 * hook is set now (or a previously-set hook filtered out namespaces
+		 * from finalPath), then we must recreate the finalPath from the
+		 * oidlist.
+		 */
+		if (object_access_hook || entry->hook_filtered)
+		{
+			pfree(entry->finalPath);
+			oldcxt = MemoryContextSwitchTo(SearchPathCacheContext);
+			entry->finalPath = finalNamespacePath(entry->oidlist,
+												  &entry->firstNS,
+												  &entry->hook_filtered);
+			MemoryContextSwitchTo(oldcxt);
+		}
+	}
+
+	*firstNS = entry->firstNS;
+	*temp_missing = entry->temp_missing;
+	*prevPathEqual = equal(prevPath, entry->finalPath);
+	if (prevPathFree)
+		list_free(prevPath);
+
+	return entry->finalPath;
+}
+
+/*
+ * recomputeNamespacePath - recompute path derived variables if needed.
+ */
+static void
+recomputeNamespacePath(void)
+{
+	Oid			roleid = GetUserId();
+	List	   *finalPath;
+	Oid			firstNS;
+	bool		temp_missing;
+	bool		prevPathEqual;
+	bool		pathChanged;
+
+	/* Do nothing if path is already valid. */
+	if (baseSearchPathValid && namespaceUser == roleid)
+		return;
+
+	finalPath = cachedNamespacePath(namespace_search_path, roleid,
+									&firstNS, &temp_missing, baseSearchPath,
+									&prevPathEqual);
+
+	/* may have been invalidated when retrieving from cache */
+	baseSearchPath = NULL;
 
-	/*
-	 * 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 unnecessarily.
-	 */
 	if (baseCreationNamespace == firstNS &&
 		baseTempCreationPending == temp_missing &&
-		equal(oidlist, baseSearchPath))
+		prevPathEqual)
 	{
 		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. */
+	baseSearchPath = finalPath;
+	baseCreationNamespace = firstNS;
+	baseTempCreationPending = temp_missing;
+
 	/* Mark the path valid. */
 	baseSearchPathValid = true;
 	namespaceUser = roleid;
@@ -3791,11 +3989,6 @@ recomputeNamespacePath(void)
 	 */
 	if (pathChanged)
 		activePathGeneration++;
-
-	/* Clean up. */
-	pfree(rawname);
-	list_free(namelist);
-	list_free(oidlist);
 }
 
 /*
@@ -3950,6 +4143,7 @@ InitTempTableNamespace(void)
 	myTempNamespaceSubID = GetCurrentSubTransactionId();
 
 	baseSearchPathValid = false;	/* need to rebuild list */
+	searchPathCacheValid = false;
 }
 
 /*
@@ -3975,6 +4169,7 @@ AtEOXact_Namespace(bool isCommit, bool parallel)
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+			searchPathCacheValid = false;
 
 			/*
 			 * Reset the temporary namespace flag in MyProc.  We assume that
@@ -4016,6 +4211,7 @@ AtEOSubXact_Namespace(bool isCommit, SubTransactionId mySubid,
 			myTempNamespace = InvalidOid;
 			myTempToastNamespace = InvalidOid;
 			baseSearchPathValid = false;	/* need to rebuild list */
+			searchPathCacheValid = false;
 
 			/*
 			 * Reset the temporary namespace flag in MyProc.  We assume that
@@ -4130,6 +4326,10 @@ assign_search_path(const char *newval, void *extra)
 	 * We mark the path as needing recomputation, but don't do anything until
 	 * it's needed.  This avoids trying to do database access during GUC
 	 * initialization, or outside a transaction.
+	 *
+	 * This does not invalidate the search path cache, so if this value had
+	 * been previously set and no syscache invalidations happened,
+	 * recomputation may not be necessary.
 	 */
 	baseSearchPathValid = false;
 }
@@ -4164,6 +4364,10 @@ InitializeSearchPath(void)
 	}
 	else
 	{
+		SearchPathCacheContext = AllocSetContextCreate(
+			TopMemoryContext, "search_path processing cache",
+			ALLOCSET_DEFAULT_SIZES);
+
 		/*
 		 * In normal mode, arrange for a callback on any syscache invalidation
 		 * of pg_namespace rows.
@@ -4173,6 +4377,7 @@ InitializeSearchPath(void)
 									  (Datum) 0);
 		/* Force search path to be recomputed on next use */
 		baseSearchPathValid = false;
+		searchPathCacheValid = false;
 	}
 }
 
@@ -4183,8 +4388,13 @@ InitializeSearchPath(void)
 static void
 NamespaceCallback(Datum arg, int cacheid, uint32 hashvalue)
 {
-	/* Force search path to be recomputed on next use */
+	/*
+	 * Force search path to be recomputed on next use, also invalidating the
+	 * search path cache (because namespace names, ACLs, or role names may
+	 * have changed).
+	 */
 	baseSearchPathValid = false;
+	searchPathCacheValid = false;
 }
 
 /*
-- 
2.34.1

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