Re: Inserting 8MB bytea: just 25% of disk perf used?
От | fkater@googlemail.com |
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Тема | Re: Inserting 8MB bytea: just 25% of disk perf used? |
Дата | |
Msg-id | 20100118160420.GF2913@comppasch2 обсуждение исходный текст |
Ответ на | Inserting 8MB bytea: just 25% of disk perf used? ("fkater@googlemail.com" <fkater@googlemail.com>) |
Список | pgsql-performance |
Hannu Krosing: > did you also test this with fsync=off ? Yes. No significant difference. > I suspect that what you are seeing is the effect of randomly writing to > the index files. While sequential write performance can be up to > 80MB/sec on modern drives, sequential writes are an order of magnitude > slower. And at your data sizes you are very likely to hit a > CHECKPOINT, which needs to do some random writes. Yes, from the server log I noticed that I hit checkpoints too early and too often. I tried the astronomical value of 1000 for checkpoint_segments to not hit a single one for the whole test run (copying 800 MB) -- even though that is no good idea in practice of course. It took even longer then. Probably because the server created a lot of 16 MB log files (about 300 in my case) which is presumly more costy (at least for the first run?) than overwriting existing files. I am not too much into that, though, since this is not a solution anyway on the long run IMHO. Thanks again. Felix
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