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Fix data-corruption hazard in WAL-logged CREATE DATABASE.

RelationCopyStorageUsingBuffer thought it could skip copyingempty pages, but of course that does not work at all, becausesubsequent blocks will be out of place.Also fix it to acquire share lock on the source buffer. It *might*be safe to not do that, but it's not very certain, and I don't thinkthis code deserves any benefit of the doubt.Dilip Kumar, per complaint from meDiscussion:https://postgr.es/m/3679800.1659654066@sss.pgh.pa.us

1 parent6390bc7 commit811203dCopy full SHA for 811203d

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src/backend/storage/buffer
- bufmgr.c

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-7

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`‎src/backend/storage/buffer/bufmgr.c`

Lines changed: 3 additions & 7 deletions

Original file line number	Diff line number	Diff line change
`@@ -3742,23 +3742,19 @@ RelationCopyStorageUsingBuffer(Relation src, Relation dst, ForkNumber forkNum,`
`3742`	`3742`	`srcBuf=ReadBufferWithoutRelcache(src->rd_node,forkNum,blkno,`
`3743`	`3743`	`RBM_NORMAL,bstrategy_src,`
`3744`	`3744`	`permanent);`
	`3745`	`+LockBuffer(srcBuf,BUFFER_LOCK_SHARE);`
`3745`	`3746`	`srcPage=BufferGetPage(srcBuf);`
`3746`		`-if (PageIsNew(srcPage)\|\|PageIsEmpty(srcPage))`
`3747`		`-{`
`3748`		`-ReleaseBuffer(srcBuf);`
`3749`		`-continue;`
`3750`		`-}`
`3751`	`3747`
`3752`	`3748`	`/* Use P_NEW to extend the destination relation. */`
`3753`	`3749`	`dstBuf=ReadBufferWithoutRelcache(dst->rd_node,forkNum,P_NEW,`
`3754`	`3750`	`RBM_NORMAL,bstrategy_dst,`
`3755`	`3751`	`permanent);`
`3756`	`3752`	`LockBuffer(dstBuf,BUFFER_LOCK_EXCLUSIVE);`
	`3753`	`+dstPage=BufferGetPage(dstBuf);`
`3757`	`3754`
`3758`	`3755`	`START_CRIT_SECTION();`
`3759`	`3756`
`3760`	`3757`	`/* Copy page data from the source to the destination. */`
`3761`		`-dstPage=BufferGetPage(dstBuf);`
`3762`	`3758`	`memcpy(dstPage,srcPage,BLCKSZ);`
`3763`	`3759`	`MarkBufferDirty(dstBuf);`
`3764`	`3760`
`@@ -3769,7 +3765,7 @@ RelationCopyStorageUsingBuffer(Relation src, Relation dst, ForkNumber forkNum,`
`3769`	`3765`	`END_CRIT_SECTION();`
`3770`	`3766`
`3771`	`3767`	`UnlockReleaseBuffer(dstBuf);`
`3772`		`-ReleaseBuffer(srcBuf);`
	`3768`	`+UnlockReleaseBuffer(srcBuf);`
`3773`	`3769`	`}`
`3774`	`3770`	`}`
`3775`	`3771`

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`‎src/backend/storage/buffer/bufmgr.c`

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