Re: vacuumdb ERROR: out of memory

Magnus Hagander wrote:
> On Tue, Feb 9, 2010 at 09:53, David Kerr <dmk@mr-paradox.net> wrote:
>> Guillaume Lelarge wrote:
>>> Le 09/02/2010 09:35, David Kerr a écrit :
>>>> Guillaume Lelarge wrote:
>>>>> Le 09/02/2010 05:49, John R Pierce a écrit :
>>>>>> David Kerr wrote:
>>>>>>>>> maintenance_work_mem = 1GB
>>>>>>>> So evidently, when it tries to actually allocate 1GB, it can't do it.
>>>>>>>> Ergo, that setting is too high for your machine.
>>>>>>>> ...
>>>>>>> seems like i've got 2GB free.
>>>>>> is this a 64bit postgres build?
>>>>>>
>>>>>> if not, you're probably running out of virtual address space in the 32
>>>>>> bit user space, which is limited to like 2gb.
>>>>>>
>>>>> IIRC, the virtual address space in 32bit platforms is 4GB.
>
> IIRC, on Linux that will be a max of 3Gb available to userspace
> processes. Certainly not 4Gb - but it could be 2.
>
>
>>>> it is a 32bit box.
>>>>
>>>>>> the other possibility, and here I'm not sure, is that
>>>>>> maintenance_work_mem is coming out of shared memory, and if so, you've
>>>>>> exceeeded your SHMMAX kernel limit.
>>>>>>
>>>>> work_mem and maintenance_work_mem are not shared memory. AFAICT, David
>>>>> need to check if the VACUUM works with a lower setting for
>>>>> maintenance_work_mem. For example, 512MB could work.
>>>>>
>>>>>
>>>> Yes, vacuum -z works with 512MB. so any idea what was causing it not to
>>>> work with 1GB?
>>>>
>>> Tom already explained that. The process couldn't get the 1GB it was
>>> allowed to use with this setting of maintenance_work_mem.
>>>
>>>
>> Well, that made sense until I freed up a lot of memory on the box. I had
>> tried it again with 2GB of free memory available to me to use. My ulimits
>> are all unlimited. So i'm wondering if there's a kernel setting I need, or
>> something similar.
>
> You may well be running out of *address space* rather than pure
> memory. PostgreSQL is failing to allocate 1Gb of *continuous* memory.
> Not just 1Gb of memory anywhere. Shared memory, for example, lives at
> a fixed location already. There may be >1Gb free in the address space,
> just not where you need it.

Ok that makes sense, it never occurred to me that malloc would require
a contiguous chunk the full size of the allocation request.


> In general, when you are starting to talk about things like 1Gb
> maintenance_work_mem, you should've switched to 64-bit a while ago :-)

Yes, I know, I actually specced out the server as 64 bit but someone
messed up and i'm making due with what I have.

>> oh, hmm, my swap is 517Megs, that probably isn't helping. Usually swap is
>> 1.5/2x available memory, isn't it? (it is for most unix's and oracle, but
>> i'm not sure about PG and linux)
>
> I don't think that affects this problem.

ok.

Thanks

Dave