Re: parallel pg_restore - WIP patch

Andrew Dunstan wrote:
>
>
> Stefan Kaltenbrunner wrote:
>> Tom Lane wrote:
>>> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>>>> Tom Lane wrote:
>>>>> Um, FKs could conflict with each other too, so that by itself isn't
>>>>> gonna fix anything.
>>>
>>>> Good point. Looks like we'll need to make a list of "can't run in
>>>> parallel with" items as well as strict dependencies.
>>>
>>> Yeah, I was just thinking about that. The current archive format
>>> doesn't really carry enough information for this. I think there
>>> are two basic solutions we could adopt:
>>>
>>> * Extend the archive format to provide some indication that "restoring
>>> this object requires exclusive access to these dependencies".
>>>
>>> * Hardwire knowledge into pg_restore that certain types of objects
>>> require exclusive access to their dependencies.
>>>
>>> The former seems more flexible, as well as more in tune with the basic
>>> design assumption that pg_restore shouldn't have a lot of knowledge
>>> about individual archive object types. But it would mean that you
>>> couldn't use parallel restore with any pre-8.4 dumps. In the long run
>>> that's no big deal, but in the short run it's annoying.
>>
>> hmm not sure how much of a problem that really is - we usually
>> recommend to use the pg_dump version of the target database anyway.
>>
>>
>>
>>
>
> We don't really need a huge amount of hardwiring as it turns out. Here
> is a version of the patch that tries to do what's needed in this area.

this one is much better - however I still seem to be able to create
deadlock scenarios with strange FK relations - ie FKs going in both
directions between two tables.

for those interested these are the timings on my 8 core testbox for my
test database:

single process restore: 169min
-m2: 101min
-m6: 64min
-m8: 63min
-m16: 56min

Stefan