When GIN changes a metapage, we WAL-log its ex-header content and never use a backup block. This reduces WAL volume since the vast majority of the metapage is unused. However, ginRedoUpdateMetapage() only restores the WAL-logged content if the metapage LSN predates the WAL record LSN. If a metapage write tore and updated the LSN but not the other content, we would fail to complete the update. Instead, unconditionally reinitialize the metapage similar to how _bt_restore_meta() handles the situation.
I found this problem by code reading and did not attempt to build a test case illustrating its practical consequences. It's possible that there's no problem in practice on account of some reason I haven't contemplated. Thanks, nm
*** a/src/backend/access/gin/ginxlog.c --- b/src/backend/access/gin/ginxlog.c *************** *** 492,504 **** ginRedoUpdateMetapage(XLogRecPtr lsn, XLogRecord *record) return; /* assume index was deleted, nothing to do */ metapage = BufferGetPage(metabuffer); ! if (!XLByteLE(lsn, PageGetLSN(metapage))) ! { ! memcpy(GinPageGetMeta(metapage), &data->metadata, sizeof(GinMetaPageData)); ! PageSetLSN(metapage, lsn); ! PageSetTLI(metapage, ThisTimeLineID); ! MarkBufferDirty(metabuffer); ! } if (data->ntuples > 0) { --- 492,503 ---- return; /* assume index was deleted, nothing to do */ metapage = BufferGetPage(metabuffer); ! GinInitMetabuffer(metabuffer); ! memcpy(GinPageGetMeta(metapage), &data->metadata, sizeof(GinMetaPageData)); ! ! PageSetLSN(metapage, lsn); ! PageSetTLI(metapage, ThisTimeLineID); ! MarkBufferDirty(metabuffer); if (data->ntuples > 0) {
-- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers