Avoid deadlocks during insertion into SP-GiST indexes.

SP-GiST's original scheme for avoiding deadlocks during concurrent index
insertions doesn't work, as per report from Hailong Li, and there isn't any
evident way to make it work completely.  We could possibly lock individual
inner tuples instead of their whole pages, but preliminary experimentation
suggests that the performance penalty would be huge.  Instead, if we fail
to get a buffer lock while descending the tree, just restart the tree
descent altogether.  We keep the old tuple positioning rules, though, in
hopes of reducing the number of cases where this can happen.

Teodor Sigaev, somewhat edited by Tom Lane

1 files changed, 15 insertions, 2 deletions

diff --git a/src/backend/access/spgist/spginsert.c b/src/backend/access/spgist/spginsert.c
index 94384acc485..f4d0fe5a0c2 100644
--- a/src/backend/access/spgist/spginsert.c
+++ b/src/backend/access/spgist/spginsert.c
@@ -45,7 +45,10 @@ spgistBuildCallback(Relation index, HeapTuple htup, Datum *values,
 	/* Work in temp context, and reset it after each tuple */
 	oldCtx = MemoryContextSwitchTo(buildstate->tmpCtx);
 
-	spgdoinsert(index, &buildstate->spgstate, &htup->t_self, *values, *isnull);
+	/* No concurrent insertions can be happening, so failure is unexpected */
+	if (!spgdoinsert(index, &buildstate->spgstate, &htup->t_self,
+					 *values, *isnull))
+		elog(ERROR, "unexpected spgdoinsert() failure");
 
 	MemoryContextSwitchTo(oldCtx);
 	MemoryContextReset(buildstate->tmpCtx);
@@ -219,7 +222,17 @@ spginsert(PG_FUNCTION_ARGS)
 
 	initSpGistState(&spgstate, index);
 
-	spgdoinsert(index, &spgstate, ht_ctid, *values, *isnull);
+	/*
+	 * We might have to repeat spgdoinsert() multiple times, if conflicts
+	 * occur with concurrent insertions.  If so, reset the insertCtx each time
+	 * to avoid cumulative memory consumption.	That means we also have to
+	 * redo initSpGistState(), but it's cheap enough not to matter.
+	 */
+	while (!spgdoinsert(index, &spgstate, ht_ctid, *values, *isnull))
+	{
+		MemoryContextReset(insertCtx);
+		initSpGistState(&spgstate, index);
+	}
 
 	SpGistUpdateMetaPage(index);