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Commit89f3973

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Fix WAL format incompatibility introduced by backpatching of52ac6cd
52ac6cd added new field to ginxlogDeletePage and was backpatched to 9.4.That led to problems when patched postgres instance applies WAL recordsgenerated by non-patched one. WAL records generated by non-patched instancedon't contain new field, which patched one is expecting to see.Thankfully, we can distinguish patched and non-patched WAL records by their datasize. If we see that WAL record is generated by non-patched instance, we skipprocessing of new field. This commit comes with some assertions. Inparticular, if it appears that on some platform struct data size didn't changethen static assertion will trigger.Reported-by: Simon RiggsDiscussion:https://postgr.es/m/CANP8%2Bj%2BK4whxf7ET7%2BgO%2BG-baC3-WxqqH%3DnV4X2CgfEPA3Yu3g%40mail.gmail.comAuthor: Alexander KorotkovReviewed-by: Simon Riggs, Alvaro HerreraBackpatch-through: 9.4
1 parent7d7435c commit89f3973

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‎src/backend/access/gin/ginxlog.c

Lines changed: 18 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -531,7 +531,24 @@ ginRedoDeletePage(XLogReaderState *record)
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page=BufferGetPage(dbuffer);
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Assert(GinPageIsData(page));
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GinPageGetOpaque(page)->flags=GIN_DELETED;
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GinPageSetDeleteXid(page,data->deleteXid);
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/*
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* deleteXid field of ginxlogDeletePage was added during backpatching.
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* But, non-backpatched instances will continue generate WAL without
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* this field. We should be able to correctly apply that. We can
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* distinguish new WAL records by size their data, because
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* ginxlogDeletePage changes its size on both 32-bit and 64-bit
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* platforms.
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*/
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StaticAssertStmt(sizeof(ginxlogDeletePage)!=
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sizeof(ginxlogDeletePageOld),
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"ginxlogDeletePage size should be changed "
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"with addition of deleteXid field");
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Assert(XLogRecGetDataLen(record)==sizeof(ginxlogDeletePage)||
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XLogRecGetDataLen(record)==sizeof(ginxlogDeletePageOld));
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if (XLogRecGetDataLen(record)==sizeof(ginxlogDeletePage))
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GinPageSetDeleteXid(page,data->deleteXid);
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PageSetLSN(page,lsn);
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MarkBufferDirty(dbuffer);
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}

‎src/include/access/ginxlog.h

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -161,6 +161,16 @@ typedef struct ginxlogDeletePage
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TransactionIddeleteXid;/* last Xid which could see this page in scan */
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}ginxlogDeletePage;
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/*
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* Previous version of ginxlogDeletePage struct, which didn't have deleteXid
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* field. Used for size comparison (see ginRedoDeletePage()).
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*/
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typedefstructginxlogDeletePageOld
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{
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OffsetNumberparentOffset;
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BlockNumberrightLink;
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}ginxlogDeletePageOld;
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#defineXLOG_GIN_UPDATE_META_PAGE 0x60
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/*

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