On Wed, 12 Nov 2014, xinxin shu wrote:
> recently we focus on 4k random write , dump transaction on every 4k
> random write op , found that , for every 4k random write , it will
> update pg epoch and pg info on OSDService::infos_oid , we find the
> below transaction will be serialized on the infos_oid , which maybe
> not friendly to 4k random write performance . i want to if there is
> any special consideration on serializing pg epoch and info update on
> infos_oid , can we shard this to pg level ?
>
> { "op_num": 1,
>
> "op_name": "omap_setkeys",
>
> "collection": "meta",
>
> "oid": "16ef7597\/infos\/head\/\/-1",
>
> "attr_lens": { "0.3c_epoch": 4,
>
> "0.3c_info": 721}},
I think we did that for simplicity without thinking about locking
parallelism.. there is no particular need to have the keys on the same
object. It's a bit awkward to make the change (since we need to read the
old scheme and write the new one), but it's nothing we haven't done
before.
Probably a better strategy is an object per PG. But before we pick a new
pg object in meta/ we should make sure this is the right strategy... we
may want something that is grouped with the PG collection and is
compatible with whatever the 'collection' concept morphs in to.
> btw , i have some question on DBObjectMap lock , currently DBObjectMap
> has several locks , cache lock , header lock
>
> for cache lock , it seems that it is lock for header cache , but
> LRUCache has an internal lock , is it a duplicated lock?
>
> for header lock, the annotation shows that it serialize the access to
> next seq and in_use set , but after checking the code , header lock
> seems not just protect the in_use and next seq . my question is what
> header_lock exactly protects?
Sam, Somnath, or Haomai would have to answer that one...
sage
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