>From 62e1c6fc679af80f8f4d26f1fe9d2fae8f430100 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Wed, 29 May 2013 15:37:05 +0200 Subject: [PATCH] Ensure that all_visible WAL records operate on an intialized page There was a race condition were lazy_scan_heap could cause all_visible records to be emitted although the page marked all visible wasn't logged in an initialized state yet causing a PANIC during WAL replay. --- src/backend/commands/vacuumlazy.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index 9d30415..4eff3c1 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -663,6 +663,31 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, /* empty pages are always all-visible */ if (!PageIsAllVisible(page)) { + /* + * There's a race condition here we need to prevent: Another + * backend might have extended the heap and PageInit'ed but + * ERRORed before filling the page with actual content. + * + * Since relation extension is not WAL logged (and we don't + * even dirty the buffer) it's quite possible that the page's + * content hasn't made it to disk yet, especially on a + * standby. During WAL replay we then could find an + * uninitialized page when trying to set the all visible flag + * which will cause a PANIC lateron. + * + * If there already is a WAL record covering this page + * (i.e. its LSN is valid) the respective record it will + * initialize the page, so we don't need to do anything in that + * case. + * + * XXX: It would be nice to use a logging method supporting + * standard buffers here since log_newpage_buffer() will write + * the full block instead of omitting the hole. + */ + if (RelationNeedsWAL(onerel) && + PageGetLSN(page) == InvalidXLogRecPtr) + log_newpage_buffer(buf); + PageSetAllVisible(page); MarkBufferDirty(buf); visibilitymap_set(onerel, blkno, buf, InvalidXLogRecPtr, -- 1.7.10.4