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Fix oversight in EvalPlanQualFetch: after failing to lock a tuple because

someone else has just updated it, we have to set priorXmax to that tuple'sxmax (ie, the XID of the other xact that updated it) before looping back toexamine the next tuple. Obviously, the next tuple in the update chain shouldhave that XID as its xmin, not the same xmin as the preceding tuple that wehad been trying to lock. The mismatch would cause the EvalPlanQual logic todecide that the tuple chain ended in a deletion, when actually there was alive tuple that should have been found.I inserted this error when recently adding logic to EvalPlanQual to make itlock tuples before returning them (as opposed to the old method in which thelock would occur much later, causing a great deal of work to be wasted if weonly then discover someone else updated it). Sigh. Per today's report fromTakahiro Itagaki of inconsistent results during pgbench runs.

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src/backend/executor
- execMain.c

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`‎src/backend/executor/execMain.c`

Lines changed: 3 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -26,7 +26,7 @@`
`26`	`26`	`*`
`27`	`27`	`*`
`28`	`28`	`* IDENTIFICATION`
`29`		`- * $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.340 2010/01/06 03:04:01 momjian Exp $`
	`29`	`+ * $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.341 2010/01/08 02:44:00 tgl Exp $`
`30`	`30`	`*`
`31`	`31`	`*-------------------------------------------------------------------------`
`32`	`32`	`*/`
`@@ -1546,6 +1546,8 @@ EvalPlanQualFetch(EState *estate, Relation relation, int lockmode,`
`1546`	`1546`	`{`
`1547`	`1547`	`/* it was updated, so look at the updated version */`
`1548`	`1548`	`tuple.t_self=update_ctid;`
	`1549`	`+/* updated row should have xmin matching this xmax */`
	`1550`	`+priorXmax=update_xmax;`
`1549`	`1551`	`continue;`
`1550`	`1552`	`}`
`1551`	`1553`	`/* tuple was deleted, so give up */`

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Commit217dc52

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`‎src/backend/executor/execMain.c`

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