diff options
| -rw-r--r-- | doc/TODO.detail/performance | 108 |
1 files changed, 105 insertions, 3 deletions
diff --git a/doc/TODO.detail/performance b/doc/TODO.detail/performance index 62b302014e8..2fbfabe4cbd 100644 --- a/doc/TODO.detail/performance +++ b/doc/TODO.detail/performance @@ -345,7 +345,7 @@ From owner-pgsql-hackers@hub.org Tue Oct 19 10:31:10 1999 Received: from renoir.op.net (root@renoir.op.net [209.152.193.4]) by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id KAA29087 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 10:31:08 -0400 (EDT) -Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.15 $) with ESMTP id KAA27535 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 10:19:47 -0400 (EDT) +Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.16 $) with ESMTP id KAA27535 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 10:19:47 -0400 (EDT) Received: from localhost (majordom@localhost) by hub.org (8.9.3/8.9.3) with SMTP id KAA30328; Tue, 19 Oct 1999 10:12:10 -0400 (EDT) @@ -454,7 +454,7 @@ From owner-pgsql-hackers@hub.org Tue Oct 19 21:25:30 1999 Received: from renoir.op.net (root@renoir.op.net [209.152.193.4]) by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id VAA28130 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 21:25:26 -0400 (EDT) -Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.15 $) with ESMTP id VAA10512 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 21:15:28 -0400 (EDT) +Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.16 $) with ESMTP id VAA10512 for <maillist@candle.pha.pa.us>; Tue, 19 Oct 1999 21:15:28 -0400 (EDT) Received: from localhost (majordom@localhost) by hub.org (8.9.3/8.9.3) with SMTP id VAA50745; Tue, 19 Oct 1999 21:07:23 -0400 (EDT) @@ -1006,7 +1006,7 @@ From pgsql-general-owner+M2497@hub.org Fri Jun 16 18:31:03 2000 Received: from renoir.op.net (root@renoir.op.net [207.29.195.4]) by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id RAA04165 for <pgman@candle.pha.pa.us>; Fri, 16 Jun 2000 17:31:01 -0400 (EDT) -Received: from hub.org (root@hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.15 $) with ESMTP id RAA13110 for <pgman@candle.pha.pa.us>; Fri, 16 Jun 2000 17:20:12 -0400 (EDT) +Received: from hub.org (root@hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.16 $) with ESMTP id RAA13110 for <pgman@candle.pha.pa.us>; Fri, 16 Jun 2000 17:20:12 -0400 (EDT) Received: from hub.org (majordom@localhost [127.0.0.1]) by hub.org (8.10.1/8.10.1) with SMTP id e5GLDaM14477; Fri, 16 Jun 2000 17:13:36 -0400 (EDT) @@ -3162,3 +3162,105 @@ Curt Sampson <cjs@cynic.net> +81 90 7737 2974 http://www.netbsd.org Don't you know, in this new Dark Age, we're all light. --XTC +From kaf@nwlink.com Fri Apr 26 14:22:39 2002 +Return-path: <kaf@nwlink.com> +Received: from doppelbock.patentinvestor.com (ip146.usw5.rb1.bel.nwlink.com [209.20.249.146]) + by candle.pha.pa.us (8.11.6/8.10.1) with ESMTP id g3QIMc400783 + for <pgman@candle.pha.pa.us>; Fri, 26 Apr 2002 14:22:38 -0400 (EDT) +Received: (from kaf@localhost) + by doppelbock.patentinvestor.com (8.11.6/8.11.2) id g3QII0l16824; + Fri, 26 Apr 2002 11:18:00 -0700 +From: Kyle <kaf@nwlink.com> +MIME-Version: 1.0 +Content-Type: text/plain; charset=us-ascii +Content-Transfer-Encoding: 7bit +Message-ID: <15561.39384.296503.501888@doppelbock.patentinvestor.com> +Date: Fri, 26 Apr 2002 11:18:00 -0700 +To: Bruce Momjian <pgman@candle.pha.pa.us> +Subject: Re: [HACKERS] Sequential Scan Read-Ahead +In-Reply-To: <200204261444.g3QEiFh11090@candle.pha.pa.us> +References: <15561.26116.817541.950416@doppelbock.patentinvestor.com> + <200204261444.g3QEiFh11090@candle.pha.pa.us> +X-Mailer: VM 6.95 under 21.1 (patch 14) "Cuyahoga Valley" XEmacs Lucid +Status: ORr + +Hey Bruce, + +I'll forward this to the list if you think they'd benefit from it. +I'm not sure it says anything about read-ahead, I think this is more a +kernel caching issue. But I've been known to be wrong in the past. +Anyway... + + +the test: + +foreach i (5 15 20 25 30 ) + echo $i + time dd bs=8k if=big_file1 of=/dev/null & + sleep $i + time dd bs=8k if=big_file1 of=/dev/null & + wait +end + +I did a couple more runs in the low range since their is a drastic +jump in elapsed (wall clock) time after doing a 6 second sleep: + + first process second process +sleep user kernel elapsed user kernel elapsed +0 sec 0.200 7.980 1:26.57 0.240 7.720 1:26.56 +3 sec 0.260 7.600 1:25.71 0.260 8.100 1:22.60 +5 sec 0.160 7.890 1:26.04 0.220 8.180 1:21.04 +6 sec 0.220 8.070 1:19.59 0.230 7.620 1:25.69 +7 sec 0.210 9.270 1:57.92 0.100 8.750 1:50.76 +8 sec 0.240 8.060 4:47.47 0.300 7.800 4:40.40 +15 sec 0.200 8.500 4:51.11 0.180 7.280 4:44.36 +20 sec 0.160 8.040 4:40.72 0.240 7.790 4:37.24 +25 sec 0.170 8.150 4:37.58 0.140 8.200 4:33.08 +30 sec 0.200 7.390 4:37.01 0.230 8.220 4:31.83 + + + +with a sleep of > 6 seconds, either the second process isn't getting +cached data or readahead is being turned off. I'd guess the former, I +don't see why read-ahead would be turned off since they're both doing +sequential operations. + +Although with 512mb of memory and the disk reading at about 22 mb/sec, +maybe we're not hitting the cache. I'd guess at least ~400 megs of +kernel cache is being used for buffering this 2 gig file. free(1) +reports: + +% free + total used free shared buffers cached +Mem: 512924 508576 4348 0 2640 477960 +-/+ buffers/cache: 27976 484948 +Swap: 527152 15864 511288 + +so shouldn't we be getting cached data even with a sleep of up to +about (400/22) 18 seconds...? Maybe I'm just in the dark on what's +really happening. I should point out that this is linux 2.4.18. + + + + +Bruce Momjian wrote: +> +> I am trying to illustrate how kernel read-ahead could be turned off in +> certain cases. +> +> --------------------------------------------------------------------------- +> +> Kyle wrote: +> > What are you trying to test, the kernel's cache vs disk speed? +> > +> > +> > Bruce Momjian wrote: +> > > +> > > Nice test. Would you test simultaneous 'dd' on the same file, perhaps +> > > with a slight delay between to the two so they don't read each other's +> > > blocks? +> > > +> > > seek() in the file will turn off read-ahead in most OS's. I am not +> > > saying this is a major issue for PostgreSQL but the numbers would be +> > > interesting. + |