Howard Chu wrote:
Tim Dyce wrote:Hi Howard, Thanks for the help :D We have been testing in ramdisk as well, to make sure that disk thrashing is not the root cause. If your searches are not running long enough to show up for profiling, increase the number of second level entries until you get something you can profile.Ah, there's a bug in your script, it's creating the 2nd-level entries with the wrong DN so the DB never had more than 250 entries. Now I've fixed that and run again and can see the behavior you're talking about. It's actually due to a particular design choice: Ordinarily at each level of the tree we keep an index tallying all of the children beneath that point. In back-bdb this index is used for subtree searches and for onelevel searches. (In back-hdb it's only used for onelevel.) However, as a write optimization, for the root entry of the DB, we don't bother to maintain this index, it's simply set to "All entries". (Otherwise in the back-bdb case, there is far too much write overhead to maintain this index.) The problem is that "All entries" is actually a range 1 to N where N is the ID of the last entry in the DB. (And 1 is the ID of the root entry.) As you add entries, N keeps increasing, but 1 stays constant. When you do a subtree search, every entryID in the corresponding index slot is checked. In this case, with a subtree search starting at the root entry, you will always be iterating through every ID from 1 thru N, even though many of those IDs have been deleted, and it takes time for BDB to return "no such object" for all the deleted IDs. If you do all of your operations under a child entry instead of the database root entry, the performance will be constant. I've already verified this with a modified copy of your test. I can post it if you wish.
Just for sake of comparison with your original test setup from http://www.openldap.org/lists/openldap-technical/201010/msg00237.htmlI tweaked the DB_CONFIG parameters to speed up the ldapadds, otherwise it takes too long to run the test. Your cache sizes etc. were all too small...
-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/
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