Add a syscache on pg_extension.oid.

An upcoming patch requires this cache so that it can track updates
in the pg_extension catalog.  So far though, the EXTENSIONOID cache
only exists in v18 and up (see 490f869d9).  We can add it in older
branches without an ABI break, if we are careful not to disturb the
numbering of existing syscache IDs.

In v16 and before, that just requires adding the new ID at the end
of the hand-assigned enum list, ignoring our convention about
alphabetizing the IDs.  But in v17, genbki.pl enforces alphabetical
order of the IDs listed in MAKE_SYSCACHE macros.  We can fake it
out by calling the new cache ZEXTENSIONOID.

Note that adding a syscache does change the required contents of the
relcache init file (pg_internal.init).  But that isn't problematic
since we blow those away at postmaster start for other reasons.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Noah Misch <noah@leadboat.com>
Security: CVE-2026-2004
Backpatch-through: 14-17

diff --git a/src/backend/utils/cache/syscache.c b/src/backend/utils/cache/syscache.c
index 945935476c159c91e821cb265f95abeff7689965..5d0cca6177c5620f395e9ca7586b719060c16afa 100644 (file)
--- a/src/backend/utils/cache/syscache.c
+++ b/src/backend/utils/cache/syscache.c
@@ -39,6 +39,7 @@
 #include "catalog/pg_description.h"
 #include "catalog/pg_enum.h"
 #include "catalog/pg_event_trigger.h"
+#include "catalog/pg_extension.h"
 #include "catalog/pg_foreign_data_wrapper.h"
 #include "catalog/pg_foreign_server.h"
 #include "catalog/pg_foreign_table.h"
@@ -994,6 +995,18 @@ static const struct cachedesc cacheinfo[] = {
                        0
                },
                2
+       },
+       /* intentionally out of alphabetical order, to avoid an ABI break: */
+       {ExtensionRelationId,           /* EXTENSIONOID */
+               ExtensionOidIndexId,
+               1,
+               {
+                       Anum_pg_extension_oid,
+                       0,
+                       0,
+                       0
+               },
+               2
        }
 };
 

diff --git a/src/include/utils/syscache.h b/src/include/utils/syscache.h
index 27c892d24c5b9f636042e7cd0e2be9ffa7518926..bffa8c45b5eecb0e142223e0f3b469ee58dbc2a9 100644 (file)
--- a/src/include/utils/syscache.h
+++ b/src/include/utils/syscache.h
@@ -109,9 +109,11 @@ enum SysCacheIdentifier
        TYPENAMENSP,
        TYPEOID,
        USERMAPPINGOID,
-       USERMAPPINGUSERSERVER
+       USERMAPPINGUSERSERVER,
+       /* intentionally out of alphabetical order, to avoid an ABI break: */
+       EXTENSIONOID
 
-#define SysCacheSize (USERMAPPINGUSERSERVER + 1)
+#define SysCacheSize (EXTENSIONOID + 1)
 };
 
 extern void InitCatalogCache(void);