postgres.git / summary / log / commit / refs

commit    4fd05bb55b40a3c9dde2b19942f275fc31b5225a
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Mon Apr 01 20:08:15 2019 +0000

    Fix deadlock in heap_compute_xid_horizon_for_tuples().
    
    We can't call code that uses syscache while we hold buffer locks
    on a catalog relation.  If passed such a relation, just fall back
    to the general effective_io_concurrency GUC rather than trying to
    look up the containing tablespace's IO concurrency setting.
    
    We might find a better way to control prefetching in follow-up
    work, but for now this is enough to avoid the deadlock introduced
    by commit 558a9165e0.
    
    Reviewed-by: Andres Freund
    Diagnosed-by: Peter Geoghegan
    Discussion: https://postgr.es/m/CA%2BhUKGLCwPF0S4Mk7S8qw%2BDK0Bq65LueN9rofAA3HHSYikW-Zw%40mail.gmail.com
    Discussion: https://postgr.es/m/962831d8-c18d-180d-75fb-8b842e3a2742%40chrullrich.net


 src/backend/access/heap/heapam.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index de5bb9194e3..05ceb6550d5 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -6976,8 +6976,15 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
 	 * more prefetching in this case, too. It may be that this formula is too
 	 * simplistic, but at the moment there is no evidence of that or any idea
 	 * about what would work better.
+	 *
+	 * Since the caller holds a buffer lock somewhere in rel, we'd better make
+	 * sure that isn't a catalog relation before we call code that does
+	 * syscache lookups, to avoid risk of deadlock.
 	 */
-	io_concurrency = get_tablespace_io_concurrency(rel->rd_rel->reltablespace);
+	if (IsCatalogRelation(rel))
+		io_concurrency = effective_io_concurrency;
+	else
+		io_concurrency = get_tablespace_io_concurrency(rel->rd_rel->reltablespace);
 	prefetch_distance = Min((io_concurrency) + 10, MAX_IO_CONCURRENCY);
 
 	/* Start prefetching. */


[parent: 12d46ac392d0]