This would allow them to be run in parallel, yes. Being in separate databases means extra last-minute checks for existence or security (CYA for if deletes get missed) are skipped as interwiki links are generated, but overall not a big deal and an expected loss as part of the interwiki search.On Wed, Sep 9, 2015 at 10:11 AM, Kevin Smith <ksmith@wikimedia.org> wrote:Would this help if we wanted to simultaneously search multiple wikis, or are those in separate databases so it would have no effect?
Kevin Smith
Agile Coach, Wikimedia FoundationOn Wed, Sep 9, 2015 at 5:18 AM, David Causse <dcausse@wikimedia.org> wrote:Thanks Erik!
This is very promising and it opens a lot of new possibilities.
Guessing the gain is pretty hard but I think we run many small requests where network overhead is quite high compared to the actual work done by elastic. This would definitely help.
Le 08/09/2015 21:01, Erik Bernhardson a écrit :
The php engine used in prod by the wmf, hhvm, has built in support for shared (non-preemptive) concurrency via async/await keywords[1][2]. Over the weekend i spent some time converting the Elastica client library we use to work asynchronously, which would essentially let us continue on performing other calculations in the web request while network requests are processing. I've only ported over the client library[3], not the CirrusSearch code. Also this is not a complete port, there are a couple code paths that work but most of the test suite still fails.
The most obvious place we could see a benefit from this is when multiple queries are issued to elasticsearch from a single web request. If the second query doesn't depend on the results of the first it can be issued in parallel. This is actually somewhat common use case, for example doing a full text and a title search in the same request. I'm wary of making much of a guess in terms of actual latency reduction we could expect, but maybe on the order of 50 to 100 ms in cases which we currently perform requests serially and we have enough work to process. Really its hard to say at this point.
In addition to making some existing code faster, having the ability to do multiple network operations in an async manner opens up other possibilities when we are implementing things in the future. In closing, this currently isn't going anywhere it was just something interesting to toy with. I think it could be quite interesting to investigate further.
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