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Re: (ITS#7667) performance degradation when using MDB_INTEGERKEY
- To: openldap-its@OpenLDAP.org
- Subject: Re: (ITS#7667) performance degradation when using MDB_INTEGERKEY
- From: email@example.com
- Date: Tue, 20 Aug 2013 21:54:46 GMT
- Auto-submitted: auto-generated (OpenLDAP-ITS)
> Content-Type: text/plain; charset=UTF-8
> Hi, I extracted a small dataset that shows the problem.
> you can download it from here:
> I modified mdb_copy.c to demonstrate the difference. copy it to source dir
> from here
> build and
> run "time ./mdb_copy foo foo2"
> after this change the flag at line 64 and run it again.
> at my computer the difference is 17s vs 1.7s for 3 million items.
This test doesn't prove the existence of a bug. You're running on a
Little-Endian machine, therefore data that is in sorted order as a string is
in hashed order when used as an integer. Your data insert turns into a
worst-case insert order in this case, causing the worst possible random access
strides through memory. Assuming the two orders to be equivalent is a pretty
common mistake for DB programmers. Microsoft has done the same thing in
ActiveDirectory, I mentioned it here a few years ago
If you had run this test on a Big-Endian machine, like SPARC, the insert order
would be identical either way, and INTEGERKEY result would have been faster.
Closing this ITS, no bug.
> On Tue, Aug 20, 2013 at 9:04 PM, Quanah Gibson-Mount <firstname.lastname@example.org>wrote:
>> --On Sunday, August 18, 2013 11:46 AM +0000 email@example.com wrote:
>> Full_Name: Roman Gershman
>>> OS: linux 3.8.0-25-generic
>>> Submission from: (NULL) (18.104.22.168)
>> Please provide further information, specifically:
>> The size of values
>> Insert order
>> Sample code if possible
>> Quanah Gibson-Mount
>> Lead Engineer
>> Zimbra, Inc
>> Zimbra :: the leader in open source messaging and collaboration
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/