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In GIN recompression code, use mmemove rather than memcpy, for vacuum.

When vacuuming a data leaf page, any compressed posting lists that are notmodified, are copied back to the buffer from a later location in the samebuffer rather than from a palloc'd copy. IOW, they are just moveddownwards in the same buffer. Because the source and destination addressescan overlap, we must use memmove rather than memcpy.Report and fix by Alexander Korotkov.

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src/backend/access/gin
- gindatapage.c

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+14

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lines changed

`‎src/backend/access/gin/gindatapage.c`

Lines changed: 14 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -753,6 +753,13 @@ ginVacuumPostingTreeLeaf(Relation indexrel, Buffer buffer, GinVacuumState *gvs)`
`753`	`753`	`* *prdata is filled with WAL information about this operation. The caller`
`754`	`754`	`* is responsible for inserting to the WAL, along with any other information`
`755`	`755`	`* about the operation that triggered this recompression.`
	`756`	`+ *`
	`757`	`+ * NOTE: The segment pointers can point directly to the same buffer, with`
	`758`	`+ * the limitation that any earlier segment must not overlap with an original,`
	`759`	`+ * later segment. In other words, some segments may point the original buffer`
	`760`	`+ * as long as you don't make any segments larger. Currently, leafRepackItems`
	`761`	`+ * satisies this rule because it rewrites all segments after the first`
	`762`	`+ * modified one, and vacuum can only make segments shorter.`
`756`	`763`	`*/`
`757`	`764`	`staticvoid`
`758`	`765`	`dataPlaceToPageLeafRecompress(Bufferbuf,disassembledLeaf*leaf,`
`@@ -798,7 +805,13 @@ dataPlaceToPageLeafRecompress(Buffer buf, disassembledLeaf *leaf,`
`798`	`805`	`if (!modified)`
`799`	`806`	`unmodifiedsize+=segsize;`
`800`	`807`	`else`
`801`		`-memcpy(ptr,seginfo->seg,segsize);`
	`808`	`+{`
	`809`	`+/*`
	`810`	`+ * Use memmove rather than memcpy, in case the segment points`
	`811`	`+ * to the same buffer`
	`812`	`+ */`
	`813`	`+memmove(ptr,seginfo->seg,segsize);`
	`814`	`+}`
`802`	`815`	`ptr+=segsize;`
`803`	`816`	`newsize+=segsize;`
`804`	`817`	`}`

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Commit398cf25

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`‎src/backend/access/gin/gindatapage.c`

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