Norbert wrote:
> Am 08.04.25 um 22:56 schrieb Norbert:
>> Hi,
>>
>> Am 08.04.25 um 12:32 schrieb Ondřej Kuzník:
>>> just a thought:
>>>
>>> It looks like you also have a "sub"string index on that attribute, all
>>> indexes for a given attribute exist in the same namespace and a
>>> substring index generates a *lot* of items. So you'll get false
>>> positives competing for slapd's attention - have you enabled 64bit
>>> hashes already ("index_hash64 on")?
>>>
>>> Should help with the contention if you haven't yet.
>>
>> I did two further tests:
>> 1) olcIndexHash64: TRUE
>> 2) olcIndexHash64: TRUE and only keeping eq for almost_uniqe_attr
>>
>> in both cases config and data was wiped and re-created with slapadd
>> I confirmed that keysize is now 64bit in the index.
>>
>>
>> mdb_stat for the index with eq,sub and 32bit index keys from a running server
>> Status of almost_uniqe_attr
>> Tree depth: 3
>> Branch pages: 256
>> Leaf pages: 47269
>> Overflow pages: 0
>> Entries: 47486472
>>
>>
>> mdb_stat for index with eq only and 64bit index keys after fresh import
>> Status of almost_uniqe_attr
>> Tree depth: 4
>> Branch pages: 261
>> Leaf pages: 41908
>> Overflow pages: 0
>> Entries: 3931262
>>
>>
>> Unfortunately there was no change in runtime. The 1200 queries still take
>> around 11s, might be even a tiny bit
>> slower with 12s.
>
> When running those 1200 filters and recording activity with perf in parallel
> I get at the top
The best way to diagnose this is to run a single search while gdb'ing slapd and
check what two IDLs
are being operated on in mdb_idl_intersection. Considering that 24% of CPU time
is in the mdb_idl_next plt,
you're seeing a ton of overhead simply from this backend being built as a
dynamic module. You might be able
to eliminate this overhead by adding -Bsymbolic to the linker invocation for
back-mdb.
> # Samples: 45K of event 'cpu-clock:pppH'
> # Event count (approx.): 11330500000
> #
> # Children Self Command Shared Object Symbol
> # ........ ........ ....... .......................
> .............................................
> #
> 41.12% 40.82% slapd back_mdb-2.5.so.0.1.14 [.] mdb_idl_next
> |
> ---mdb_idl_next
>
> 31.71% 31.55% slapd back_mdb-2.5.so.0.1.14 [.]
> mdb_idl_intersection
> |
> ---mdb_idl_intersection
>
> 24.25% 24.11% slapd back_mdb-2.5.so.0.1.14 [.] mdb_idl_next@plt
> |
> ---mdb_idl_next@plt
>
> 1.13% 0.00% slapd [kernel.kallsyms] [k]
> entry_SYSCALL_64_after_hwframe
> |
> ---entry_SYSCALL_64_after_hwframe
> |
>
>
> And when removing the second entry I get for the same 1200 filters following
> recorded
>
> # Samples: 420 of event 'cpu-clock:pppH'
> # Event count (approx.): 105000000
> #
> # Children Self Command Shared Object Symbol
> # ........ ........ ....... .......................
> .......................................
> #
> 41.90% 0.00% slapd [kernel.kallsyms] [k]
> entry_SYSCALL_64_after_hwframe
> |
> ---entry_SYSCALL_64_after_hwframe
> |
> |--41.19%--do_syscall_64
> | |
> | |--22.62%--ksys_write
>
> Thanks,
> Norbert
>
--
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/
