From: Alexander Korotkov Date: Thu, 13 Dec 2018 03:12:31 +0000 (+0300) Subject: Prevent GIN deleted pages from being reclaimed too early X-Git-Tag: REL_11_2~125 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=dd951dc34a2ecde28cd8d686cd06de1d21f474a0;p=postgresql Prevent GIN deleted pages from being reclaimed too early When GIN vacuum deletes a posting tree page, it assumes that no concurrent searchers can access it, thanks to ginStepRight() locking two pages at once. However, since 9.4 searches can skip parts of posting trees descending from the root. That leads to the risk that page is deleted and reclaimed before concurrent search can access it. This commit prevents the risk of above by waiting for every transaction, which might wait to reference this page, to finish. Due to binary compatibility we can't change GinPageOpaqueData to store corresponding transaction id. Instead we reuse page header pd_prune_xid field, which is unused in index pages. Discussion: https://postgr.es/m/31a702a.14dd.166c1366ac1.Coremail.chjischj%40163.com Author: Andrey Borodin, Alexander Korotkov Reviewed-by: Alexander Korotkov Backpatch-through: 9.4 --- diff --git a/src/backend/access/gin/README b/src/backend/access/gin/README index 421b5b26d5..30c0867829 100644 --- a/src/backend/access/gin/README +++ b/src/backend/access/gin/README @@ -304,12 +304,10 @@ the lock on next page has been acquired. The downlink is more tricky. A search descending the tree must release the lock on the parent page before locking the child, or it could deadlock with a concurrent split of the child page; a page split locks the parent, while -already holding a lock on the child page. However, posting trees are only -fully searched from left to right, starting from the leftmost leaf. (The -tree-structure is only needed by insertions, to quickly find the correct -insert location). So as long as we don't delete the leftmost page on each -level, a search can never follow a downlink to page that's about to be -deleted. +already holding a lock on the child page. So, deleted page cannot be reclaimed +immediately. Instead, we have to wait for every transaction, which might wait +to reference this page, to finish. Corresponding processes must observe that +the page is marked deleted and recover accordingly. The previous paragraph's reasoning only applies to searches, and only to posting trees. To protect from inserters following a downlink to a deleted diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c index 0a32182dd7..64dd1a6486 100644 --- a/src/backend/access/gin/ginutil.c +++ b/src/backend/access/gin/ginutil.c @@ -309,12 +309,7 @@ GinNewBuffer(Relation index) */ if (ConditionalLockBuffer(buffer)) { - Page page = BufferGetPage(buffer); - - if (PageIsNew(page)) - return buffer; /* OK to use, if never initialized */ - - if (GinPageIsDeleted(page)) + if (GinPageIsRecyclable(BufferGetPage(buffer))) return buffer; /* OK to use */ LockBuffer(buffer, GIN_UNLOCK); diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c index bdeb0bf4f5..96609835ee 100644 --- a/src/backend/access/gin/ginvacuum.c +++ b/src/backend/access/gin/ginvacuum.c @@ -157,6 +157,9 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn page = BufferGetPage(dBuffer); rightlink = GinPageGetOpaque(page)->rightlink; + /* For deleted page remember last xid which could knew its address */ + GinPageSetDeleteXid(page, ReadNewTransactionId()); + /* * Any insert which would have gone on the leaf block will now go to its * right sibling. @@ -213,6 +216,7 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn data.parentOffset = myoff; data.rightLink = GinPageGetOpaque(page)->rightlink; + data.deleteXid = GinPageGetDeleteXid(page); XLogRegisterData((char *) &data, sizeof(ginxlogDeletePage)); @@ -732,7 +736,7 @@ ginvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats) LockBuffer(buffer, GIN_SHARE); page = (Page) BufferGetPage(buffer); - if (PageIsNew(page) || GinPageIsDeleted(page)) + if (GinPageIsRecyclable(page)) { Assert(blkno != GIN_ROOT_BLKNO); RecordFreeIndexPage(index, blkno); diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c index b626a219de..b84ecf2ab1 100644 --- a/src/backend/access/gin/ginxlog.c +++ b/src/backend/access/gin/ginxlog.c @@ -531,6 +531,7 @@ ginRedoDeletePage(XLogReaderState *record) page = BufferGetPage(dbuffer); Assert(GinPageIsData(page)); GinPageGetOpaque(page)->flags = GIN_DELETED; + GinPageSetDeleteXid(page, data->deleteXid); PageSetLSN(page, lsn); MarkBufferDirty(dbuffer); } diff --git a/src/include/access/ginblock.h b/src/include/access/ginblock.h index 553566529a..f626c40ae3 100644 --- a/src/include/access/ginblock.h +++ b/src/include/access/ginblock.h @@ -10,6 +10,7 @@ #ifndef GINBLOCK_H #define GINBLOCK_H +#include "access/transam.h" #include "storage/block.h" #include "storage/itemptr.h" #include "storage/off.h" @@ -127,6 +128,15 @@ typedef struct GinMetaPageData #define GinPageRightMost(page) ( GinPageGetOpaque(page)->rightlink == InvalidBlockNumber) +/* + * We should reclaim deleted page only once every transaction started before + * its deletion is over. + */ +#define GinPageGetDeleteXid(page) ( ((PageHeader) (page))->pd_prune_xid ) +#define GinPageSetDeleteXid(page, xid) ( ((PageHeader) (page))->pd_prune_xid = xid) +#define GinPageIsRecyclable(page) ( PageIsNew(page) || (GinPageIsDeleted(page) \ + && TransactionIdPrecedes(GinPageGetDeleteXid(page), RecentGlobalXmin))) + /* * We use our own ItemPointerGet(BlockNumber|OffsetNumber) * to avoid Asserts, since sometimes the ip_posid isn't "valid" diff --git a/src/include/access/ginxlog.h b/src/include/access/ginxlog.h index 64a3c9e18b..b2f3126aa8 100644 --- a/src/include/access/ginxlog.h +++ b/src/include/access/ginxlog.h @@ -158,6 +158,7 @@ typedef struct ginxlogDeletePage { OffsetNumber parentOffset; BlockNumber rightLink; + TransactionId deleteXid; /* last Xid which could see this page in scan */ } ginxlogDeletePage; #define XLOG_GIN_UPDATE_META_PAGE 0x60