"Kevin Grittner" <kevin.gritt...@wicourts.gov> wrote: >> Tom Lane wrote: >> Hmm, why is that patch the one posted for review, when several >> better versions were already discussed? See thread starting here: >> http://archives.postgresql.org/pgsql-hackers/2011-07/msg00028.php > > The patch I reviewed was added to the CF app before the post you > cite was written. I didn't see it in following the links > (probably because it crossed a month boundary). Thanks for > pointing that out; I'll update the CF app and review the later > versions. The first patch Tom posted was a clear improvement on Heikki's original patch, and performed slightly better. The second patch Tom posted makes the patch more robust in the face of changes to the structure, but reduces the performance benefit on the dictionary, and performs very close to the unpatched version for samples of English text. If anything, it seems to be slower with real text, but the difference is so small it might be noise. (The dictionary tests are skewed toward longer average word length than typically found in actual readable text.) I wonder whether the code for the leading, unaligned portion of the data could be written such that it was effectively unrolled and the length resolved at compile time rather than figured out at run time for every call to the function. That would solve the robustness issue without hurting performance. If we don't do something like that, this patch doesn't seem worth applying. Heikki's second version, a more radical revision optimized for 64 bit systems, blows up on a 32 bit compile, writing off the end of the structure. Personally, I'd be OK with sacrificing some performance for 32 bit systems to get better performance on 64 bit systems, since people who care about performance generally seem to be on 64 bit builds these days -- but it has to run. Given Tom's reservations about this approach, I don't know whether Heikki is interested in fixing the crash so it can be benchmarked. Heikki? I will do a set of more carefully controlled performance tests on whatever versions are still in the running after we sort out the issues above. -Kevin
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