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Antw: Re: lmdb memory usage when writing lots of data with memorymap option
>>> Howard Chu <hyc@symas.com> schrieb am 15.01.2014 um 23:10 in Nachricht
<52D7076B.3020003@symas.com>:
> Luc Vlaming wrote:
>> Hi,
>>
>> Currently I am creating support for using LMDB as a new storage backend for
>> one of our products.
>> At the moment I am testing import bulk data into lmdb using transactions
> that
>> span a single record of 10MB. The total db size afterwards is 5GB. I also
>> tested with records of 1MB.
>>
>> I noticed a very odd thing: when using the MDB_WRITEMAP option, memory usage
>> grows very quickly and linear with the amount of data stored into the
>> database. (memory usage ends up a bit higher than 5GB). when not using
Maybe for the future make a difference between virtual memory usage and real (resident) memory usage. Especially for Linux this makes a big difference, because a malloc(1GB) actually does not consume any memory until it is actually used.
There's also the "pmap" Utility that can show the detailed difference. For example my small (bdb) slapd has:
# pmap 3668
3668: slapd
START SIZE RSS PSS DIRTY SWAP PERM MAPPING
[...]
00007f601a7f4000 8192K 120K 120K 120K 0K rw-p [anon]
[...]
00007f603db4c000 18320K 184K 184K 84K 0K rw-s /var/lib/ldap/__db.003
[...]
Total: 808004K 29768K 28657K 27016K 32040K
So of 800MB virtual memory there is only 30MB actually in use...
>> MDB_WRITEMAP, however, memory usage stays very low. Does anyone have a
>> suggestion what might be wrong and what causes such different behaviour with
>> and without using the memorymap option?
>
> There is nothing wrong. It is simply writing to the shared memory map.
Off-topic: I can remember a statement of the late 80ies where a programmer claimed the 32-bit address space is so large that one does not have to care about garbage collection in virtual address space; just use new addresses. I think even with 64 bit one should always try not to waste address space.
Regards,
Ulrich
>
> --
> -- Howard Chu
> CTO, Symas Corp. http://www.symas.com
> Director, Highland Sun http://highlandsun.com/hyc/
> Chief Architect, OpenLDAP http://www.openldap.org/project/