Hi hackers,
Now that we have some optimized linear search routines [0], I thought I'd
quickly check whether we could use them elsewhere. To start, I took
another look at a previously posted patch [1] and noticed two potentially
useful applications of pg_lfind32(). The attached patches replace the
open-coded linear searches with calls to pg_lfind32(). I haven't done any
performance analysis with these patches yet, and the overall impact might
be limited, but it seemed like low-hanging fruit.
I'm hoping to spend a bit more time looking for additional applications of
the pg_lfind*() suite of functions (and anywhere else where SIMD might be
useful, really). If you have any ideas in mind, I'm all ears.
[0]
https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/include/port/pg_lfind.h
[1] https://postgr.es/m/20220802221301.GA742739%40nathanxps13
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From 1ea31af477d66557fdbc5f83a5bdacadd6159a9d Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandboss...@gmail.com>
Date: Thu, 1 Sep 2022 11:23:15 -0700
Subject: [PATCH v1 1/2] use optimized linear search in
TransactionIdIsInProgress
---
src/backend/storage/ipc/procarray.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 0555b02a8d..a8b7b65518 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -58,6 +58,7 @@
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "pgstat.h"
+#include "port/pg_lfind.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/spin.h"
@@ -1586,14 +1587,9 @@ TransactionIdIsInProgress(TransactionId xid)
*/
topxid = SubTransGetTopmostTransaction(xid);
Assert(TransactionIdIsValid(topxid));
- if (!TransactionIdEquals(topxid, xid))
- {
- for (int i = 0; i < nxids; i++)
- {
- if (TransactionIdEquals(xids[i], topxid))
- return true;
- }
- }
+ if (!TransactionIdEquals(topxid, xid) &&
+ pg_lfind32(topxid, xids, nxids))
+ return true;
cachedXidIsNotInProgress = xid;
return false;
--
2.25.1
>From d82f9b1a6e3f41e434bb5826d277269b891c9882 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandboss...@gmail.com>
Date: Thu, 1 Sep 2022 11:29:38 -0700
Subject: [PATCH v1 2/2] use optimized linear search in XidIsConcurrent
---
src/backend/storage/lmgr/predicate.c | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 5136da6ea3..f287ddfa73 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -202,6 +202,7 @@
#include "access/xlog.h"
#include "miscadmin.h"
#include "pgstat.h"
+#include "port/pg_lfind.h"
#include "storage/bufmgr.h"
#include "storage/predicate.h"
#include "storage/predicate_internals.h"
@@ -4065,7 +4066,6 @@ static bool
XidIsConcurrent(TransactionId xid)
{
Snapshot snap;
- uint32 i;
Assert(TransactionIdIsValid(xid));
Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny()));
@@ -4078,13 +4078,7 @@ XidIsConcurrent(TransactionId xid)
if (TransactionIdFollowsOrEquals(xid, snap->xmax))
return true;
- for (i = 0; i < snap->xcnt; i++)
- {
- if (xid == snap->xip[i])
- return true;
- }
-
- return false;
+ return pg_lfind32(xid, snap->xip, snap->xcnt);
}
bool
--
2.25.1
