On Wed, Oct 1, 2014 at 2:46 PM, Daniel Kinzler daniel.kinzler@wikimedia.de wrote:

We currently use memcached to share cached objects across wikis, most importantly, entity objects (like data items). Ori suggested we should look into alternatives. This is what he wrote:

[21:15] <ori> I was wondering if you think the way you use memcached is optimal (this sounds like a loaded question but I mean it sincerely). And if not, I was going to propose that you identify an optimal distributed object store, and I was also going to offer to help push for procurement and deployment of such a service on the WMF cluster. [21:17] <ori> memcached is a bit of a black box. it is very difficult to get comprehensible metrics about how much space and bandwidth you're utilizing, especially when your data is mixed up with everything else that goes into memcached [21:18] <ori> and the fact that you're serializing objects using php serialize() rather than simple values makes it even harder, because it means that you can only really poke around from php with wikidata code available

The other major problem with memcache is that it doesn't support complex data structures like lists, queues, sets, or maps, so when you want to do things like, say, push or pop an item from a queue, you end up having to retrieve the entire collection, unserialize it, manipulate it locally, re-serialize it, and transmit it back in its entirety.

Just food for thought, for now... any suggestions for a shared object store?

I'm embarrassed to say that I don't know nearly enough about Wikidata to be able to make a recommendation. Where would you recommend I look if I wanted to understand the caching architecture?

Hey,

We use two CachingEntityRevisionLookup nested into each other: the

outer-most uses a HashBagOStuff to implement in-process caching, the second level uses memcached.

It is odd to have two different decorator instances for caching around th EntityRevisionLookup. I suggest to have only a single decorator for caching, which writes to a caching interface. Then this caching interface can have an implementation what uses multiple caches, and perhaps have a decorator on that level.

Cheers

-- Jeroen De Dauw - http://www.bn2vs.com Software craftsmanship advocate Evil software architect at Wikimedia Germany ~=[,,_,,]:3

On 10/02/2014 09:22 AM, Nikolas Everett wrote:

On Thu, Oct 2, 2014 at 12:45 AM, Ori Livneh <ori@wikimedia.org mailto:ori@wikimedia.org> wrote:

On Wed, Oct 1, 2014 at 2:46 PM, Daniel Kinzler
<daniel.kinzler@wikimedia.de <mailto:daniel.kinzler@wikimedia.de>> wrote:

    We currently use memcached to share cached objects across wikis, most
    importantly, entity objects (like data items). Ori suggested we
    should look into
    alternatives. This is what he wrote:

    [21:15] <ori> I was wondering if you think the way you use memcached
    is optimal
    (this sounds like a loaded question but I mean it sincerely). And if
    not, I was
    going to propose that you identify an optimal distributed object
    store, and I
    was also going to offer to help push for procurement and deployment
    of such a
    service on the WMF cluster.
    [21:17] <ori> memcached is a bit of a black box. it is very
    difficult to get
    comprehensible metrics about how much space and bandwidth you're
    utilizing,
    especially when your data is mixed up with everything else that goes
    into memcached
    [21:18] <ori> and the fact that you're serializing objects using php
    serialize()
    rather than simple values makes it even harder, because it means
    that you can
    only really poke around from php with wikidata code available


The other major problem with memcache is that it doesn't support complex
data structures like lists, queues, sets, or maps, so when you want to
do things like, say, push or pop an item from a queue, you end up having
to retrieve the entire collection, unserialize it, manipulate it
locally, re-serialize it, and transmit it back in its entirety.

Use more Redis maybe?

Or use actual storage.