Hi! On Thu, Dec 6, 2012 at 5:44 AM, Tomas Vondra <t...@fuzzy.cz> wrote:
> Then I've run a simple benchmarking script, and the results are not as > good as I expected, actually I'm getting much worse performance than > with the original GIN index. > > The following table contains the time of loading the data (not a big > difference), and number of queries per minute for various number of > words in the query. > > The queries looks like this > > SELECT id FROM messages > WHERE body_tsvector @@ plainto_tsquery('english', 'word1 word2 ...') > > so it's really the simplest form of FTS query possible. > > without patch | with patch > -------------------------------------------- > loading 750 sec | 770 sec > 1 word 1500 | 1100 > 2 words 23000 | 9800 > 3 words 24000 | 9700 > 4 words 16000 | 7200 > -------------------------------------------- > > I'm not saying this is a perfect benchmark, but the differences (of > querying) are pretty huge. Not sure where this difference comes from, > but it seems to be quite consistent (I usually get +-10% results, which > is negligible considering the huge difference). > > Is this an expected behaviour that will be fixed by another patch? > Another patches which significantly accelerate index search will be provided. This patch changes only GIN posting lists/trees storage. However, it wasn't expected that this patch significantly changes index scan speed in any direction. The database contains ~680k messages from the mailing list archives, > i.e. about 900 MB of data (in the table), and the GIN index on tsvector > is about 900MB too. So the whole dataset nicely fits into memory (8GB > RAM), and it seems to be completely CPU bound (no I/O activity at all). > > The configuration was exactly the same in both cases > > shared buffers = 1GB > work mem = 64 MB > maintenance work mem = 256 MB > > I can either upload the database somewhere, or provide the benchmarking > script if needed. Unfortunately, I can't reproduce such huge slowdown on my testcases. Could you share both database and benchmarking script? ------ With best regards, Alexander Korotkov.