Commitc4a2041

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Handle lack of DSM slots in parallel btree build, take 2.

Commit74618e7 added a new check intended to fix a bug, but putit in the wrong place so that parallel btree build was alwaysdisabled. Do the check after we've actually tried to createa DSM segment. Back-patch to 11, like the earlier commit.Reviewed-by: Peter GeogheganDiscussion:https://postgr.es/m/CAH2-WzmDABkJzrNnvf%2BOULK-_A_j9gkYg_Dz-H62jzNv4eKQTw%40mail.gmail.com

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+10

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Lines changed: 10 additions & 8 deletions

Original file line number	Diff line number	Diff line change
`@@ -1257,14 +1257,6 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)`
`1257`	`1257`	`pcxt=CreateParallelContext("postgres","_bt_parallel_build_main",`
`1258`	`1258`	`request, true);`
`1259`	`1259`
`1260`		`-/* If no DSM segment was available, back out (do serial build) */`
`1261`		`-if (pcxt->seg==NULL)`
`1262`		`-{`
`1263`		`-DestroyParallelContext(pcxt);`
`1264`		`-ExitParallelMode();`
`1265`		`-return;`
`1266`		`-}`
`1267`		`-`
`1268`	`1260`	`scantuplesortstates=leaderparticipates ?request+1 :request;`
`1269`	`1261`
`1270`	`1262`	`/*`
`@@ -1308,6 +1300,16 @@ _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request)`
`1308`	`1300`	`/* Everyone's had a chance to ask for space, so now create the DSM */`
`1309`	`1301`	`InitializeParallelDSM(pcxt);`
`1310`	`1302`
	`1303`	`+/* If no DSM segment was available, back out (do serial build) */`
	`1304`	`+if (pcxt->seg==NULL)`
	`1305`	`+{`
	`1306`	`+if (IsMVCCSnapshot(snapshot))`
	`1307`	`+UnregisterSnapshot(snapshot);`
	`1308`	`+DestroyParallelContext(pcxt);`
	`1309`	`+ExitParallelMode();`
	`1310`	`+return;`
	`1311`	`+}`
	`1312`	`+`
`1311`	`1313`	`/* Store shared build state, for which we reserved space */`
`1312`	`1314`	`btshared= (BTShared*)shm_toc_allocate(pcxt->toc,estbtshared);`
`1313`	`1315`	`/* Initialize immutable state */`

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