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 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?

Hi, If it was simply writing to the memory map, shouldn't memory usage decrease as soon as everything is written?

The memory usage continuous to be high for as long as the database is open, even if the program just waits afterwards. Is that to be expected as well? Because that would mean that the process would simply run out of memory if more data is writting than the machine has as ram.

Regards, Luc Met vriendelijke groeten, Luc Vlaming KXA Software Innovations voorheen Dysi Software Innovations bezoekadres: Hoendiep Noordzijde 21 9843TG, Grijpskerk Luc Vlaming tel: 06 16 353 426 email: vlaming(a)softwareinnovations.nl <mailto:vlaming@softwareinnovations.nl> url: www.softwareinnovations.nl <http://www.softwareinnovations.nl/> On Wed, Jan 15, 2014 at 11:10 PM, Howard Chu <hyc(a)symas.com <mailto:hyc@symas.com>> wrote: 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 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. -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/__project/ <http://www.openldap.org/project/>

>>> Howard Chu <hyc(a)symas.com&gt; schrieb am 15.01.2014 um 23:10 in Nachricht <52D7076B.3020003(a)symas.com&gt;: > 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/

>> Howard Chu <hyc(a)symas.com&gt; schrieb am 16.01.2014 um 11:03 in Nachricht

Ulrich Windl wrote: > 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. Wow, good thing you're here to remind us of these little details, I would never have thought of that! What on earth will we do now? Oh wait, right in the LMDB design paper, there's a discussion of garbage collection. Someone must have thought of it already, after all. You're the worst kind of fool, one who believes he knows more than he actually does, in a world where it's trivially easy to acquire the actual facts.

-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/