Re: [PERFORM] insert speed - Mac OSX vs Redhat
On 16/01/2004, at 2:44 AM, Tom Lane wrote: ... As noted elsewhere, it's highly likely that this has nothing to do with the OS, and everything to do with write caching in the disks being used. I assume you are benchmarking small individual transactions (one insert per xact). In such scenarios it's essentially impossible to commit more than one transaction per revolution of the WAL disk, because you have to write the same WAL disk page repeatedly and wait for it to get down to the platter. When you get results that are markedly in excess of the disk RPM figure, it's proof positive that the disk is lying about write complete (or that you don't have fsync on). Tom, thanks for this explanation - we'll check this out straight away, but it would explain a lot. ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PERFORM] insert speed - Mac OSX vs Redhat
Syd <[EMAIL PROTECTED]> writes: > However, with postgres 7.4 on Mac OSX 10.2.3, we're getting an amazing > 500 inserts per second. > We can only put this down to the OS. As noted elsewhere, it's highly likely that this has nothing to do with the OS, and everything to do with write caching in the disks being used. I assume you are benchmarking small individual transactions (one insert per xact). In such scenarios it's essentially impossible to commit more than one transaction per revolution of the WAL disk, because you have to write the same WAL disk page repeatedly and wait for it to get down to the platter. When you get results that are markedly in excess of the disk RPM figure, it's proof positive that the disk is lying about write complete (or that you don't have fsync on). The only way to get better performance and still have genuine ACID behavior is to gang multiple insertions per WAL write. You can do multiple insertions per transaction, or if you are doing several insertion transactions in parallel, you can try to commit them all in one write (experiment with the commit_delay and commit_siblings parameters). > BTW, on the same hardware that postgres is running on to get 50 inserts > per sec, MySQL (4.0.17) is getting an almost unbelievable 5,500 inserts > per second. I'll bet a good lunch that MySQL is not being ACID compliant in this test. Are you using a transaction-safe table type (InnoDB) and committing after every insert? If you don't in fact care about ACID safety, turn off fsync in Postgres so that you have an apples-to-apples comparison (or at least apples-to-oranges rather than apples-to-cannonballs). regards, tom lane ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
Re: [PERFORM] insert speed - Mac OSX vs Redhat
> On a variety of hardware with Redhat, and versions of postgres, we're > not getting much better than 50 inserts per second. This is prior to > moving WAL to another disk, and fsync is on. > > However, with postgres 7.4 on Mac OSX 10.2.3, we're getting an amazing > 500 inserts per second. > > We can only put this down to the OS. ^^^ You haven't really produced much evidence to support that statement. Given that the differences in performance between Postgres running on *BSD and Linux on Intel hardware are not large at all, it seems to be almost certainly false in fact. It may of course be due to some settings of the different OSes, but not the OSes themselves. It would help if you gave a straight PG7.4 comparison with hardware specs as well, and config file differences if any. One thought: assuming the Apple has IDE disks, then the disks probably have write caching turned on, which is good for speed, but not crash-safe. matt ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
[PERFORM] insert speed - Mac OSX vs Redhat
I've read most of the threads on insert speed in this list and wanted to share some interesting observations and a question. We've been benchmarking some dbs to implement Bayesian processing on an email server. This involves frequent insert and updates to the following table: create table bayes_token ( username varchar(200) not null default '', token varchar(200) not null default '', spam_count integer not null default 0, ham_count integer not null default 0, atime integer not null default 0, primary key (username, token)); On a variety of hardware with Redhat, and versions of postgres, we're not getting much better than 50 inserts per second. This is prior to moving WAL to another disk, and fsync is on. However, with postgres 7.4 on Mac OSX 10.2.3, we're getting an amazing 500 inserts per second. We can only put this down to the OS. Can anyone shed light on why Redhat appears to be so much poorer than Mac OS X in supporting postgres insert transactions? Or why MacOS appears to be so much better? BTW, on the same hardware that postgres is running on to get 50 inserts per sec, MySQL (4.0.17) is getting an almost unbelievable 5,500 inserts per second. -SL ---(end of broadcast)--- TIP 9: the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
