postgrespro.git / summary / log / commit / refs

commit    2f39106a209e647d7b1895331fca115f9bb6ec8d
Author:   Alexander Korotkov <akorotkov@postgresql.org>
Date:     Sat Sep 22 13:22:30 2018 +0000

    Replace CAS loop with single TAS in ProcArrayGroupClearXid()
    
    Single pg_atomic_exchange_u32() is expected to be faster than loop of
    pg_atomic_compare_exchange_u32().  Also, it would be consistent with
    clog group update code.
    
    Discussion: https://postgr.es/m/CAPpHfdtxLsC-bqfxFcHswZ91OxXcZVNDBBVfg9tAWU0jvn1tQA%40mail.gmail.com
    Reviewed-by: Amit Kapila


 src/backend/storage/ipc/procarray.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index bd20497d81..bf2f4dbed2 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -542,14 +542,8 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
 	 * group XID clearing, saving a pointer to the head of the list.  Trying
 	 * to pop elements one at a time could lead to an ABA problem.
 	 */
-	while (true)
-	{
-		nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
-		if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
-										   &nextidx,
-										   INVALID_PGPROCNO))
-			break;
-	}
+	nextidx = pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,
+									 INVALID_PGPROCNO);
 
 	/* Remember head of list so we can perform wakeups after dropping lock. */
 	wakeidx = nextidx;


[parent: db361db2fce7]