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Protect against torn pages when deleting GIN list pages.

To-be-deleted list pages contain no useful information, as they are beingdeleted, but we must still protect the writes from being torn by a crashafter a partial write. To do that, re-initialize the pages on WAL replay.Jeff Janes caught this with a test program to test partial writes.Backpatch to all supported versions.

1 parentcd7df10 commit3457292Copy full SHA for 3457292

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src/backend/access/gin
- ginxlog.c

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+13

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`‎src/backend/access/gin/ginxlog.c`

Lines changed: 13 additions & 13 deletions

Original file line number	Diff line number	Diff line change
`@@ -682,25 +682,25 @@ ginRedoDeleteListPages(XLogRecPtr lsn, XLogRecord *record)`
`682`	`682`	`* cannot get past a reader that is on, or due to visit, any page we are`
`683`	`683`	`* going to delete. New incoming readers will block behind our metapage`
`684`	`684`	`* lock and then see a fully updated page list.`
	`685`	`+ *`
	`686`	`+ * No full-page images are taken of the deleted pages. Instead, they are`
	`687`	`+ * re-initialized as empty, deleted pages. Their right-links don't need to`
	`688`	`+ * be preserved, because no new readers can see the pages, as explained`
	`689`	`+ * above.`
`685`	`690`	`*/`
`686`	`691`	`for (i=0;i<data->ndeleted;i++)`
`687`	`692`	`{`
`688`		`-Bufferbuffer=XLogReadBuffer(data->node,data->toDelete[i], false);`
	`693`	`+Bufferbuffer;`
	`694`	`+Pagepage;`
`689`	`695`
`690`		`-if (BufferIsValid(buffer))`
`691`		`-{`
`692`		`-Pagepage=BufferGetPage(buffer);`
`693`		`-`
`694`		`-if (lsn>PageGetLSN(page))`
`695`		`-{`
`696`		`-GinPageGetOpaque(page)->flags=GIN_DELETED;`
	`696`	`+buffer=XLogReadBuffer(data->node,data->toDelete[i], true);`
	`697`	`+page=BufferGetPage(buffer);`
	`698`	`+GinInitBuffer(buffer,GIN_DELETED);`
`697`	`699`
`698`		`-PageSetLSN(page,lsn);`
`699`		`-MarkBufferDirty(buffer);`
`700`		`-}`
	`700`	`+PageSetLSN(page,lsn);`
	`701`	`+MarkBufferDirty(buffer);`
`701`	`702`
`702`		`-UnlockReleaseBuffer(buffer);`
`703`		`-}`
	`703`	`+UnlockReleaseBuffer(buffer);`
`704`	`704`	`}`
`705`	`705`	`UnlockReleaseBuffer(metabuffer);`
`706`	`706`	`}`

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Commit3457292

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`‎src/backend/access/gin/ginxlog.c`

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