Re: Much slower DBI on RHEL6

Are the database tables the same size?

Do the database tables have the exact same data?

Do the database tables have the same indexes?

Perhaps one machine (wisely) chooses to scan the table because the search conditions are not specific enough for an index (which they were on the other machine).

In short, there isn't really enough information...

update: In general, it's a shame that database questions tend to talk of "meh, slow...", "fast!", "yippee, much faster!!" but omit to post timings and/or pertinent database plans (EXPLAIN PLAN variants). Also, or even especially, when the case is solved.

Comment on Re: Much slower DBI on RHEL6

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Re^2: Much slower DBI on RHEL6 by MPM (Novice) on Feb 06, 2014 at 02:44 UTC
MySQL seems to return the data just as fast as it always has, it's the fetching done by perl-DBI that seems much slower on RHEL 6 ( perl 5.10 )	[reply]
Re^3: Much slower DBI on RHEL6 by Anonymous Monk on Feb 06, 2014 at 10:20 UTC
Perl 5.10 IIRC was one of the less optimised Perl versions. I think some benchmarks put it 20-50% slower than 5.8. 5.12 and 5.14 improved the speed much. (Sorry, no sources to back this up at this time.)	[reply]
Re^4: Much slower DBI on RHEL6 by chromatic (Archbishop) on Feb 06, 2014 at 19:04 UTC
That's exactly right. Perl 5.10.0 accidentally disabled a list assignment optimization. Perl 5.10.1 re-enabled that optimization and a lot of functions which perform list assignment from `@_` run faster under 5.10.1 than they did with 5.10.0.	[reply] [d/l]
Re^5: Much slower DBI on RHEL6 by Anonymous Monk on Feb 06, 2014 at 20:21 UTC
Re^3: Much slower DBI on RHEL6 by McA (Priest) on Feb 06, 2014 at 11:08 UTC
Hi, this thread is very interesting. How have you measured that mysql is gathering the informations at the same speed? Can you present the mysql version numbers on the different distributions? Have you checked whether the same query plan is used by mysql? Best regards McA P.S.: You use the same hardware for RHEL4 and RHEL6 and the same Linux config?	[reply]
Re^2: Much slower DBI on RHEL6 by MPM (Novice) on Feb 05, 2014 at 23:27 UTC
It is the exact same data... same table structure, etc... the data was dumped on the RHEL 4 and imported onto the RHEL 6 machine.	[reply]


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