Well, you are free to suggest a better advice. In the case of shards
splitting into different servers, Quarry will have to implement a server /
database selector [1], and processing data from two databases in a single
query may not be possible at all, like currently in the case of tools-db
and replicas, where all inter-host joins must happen in application space.
In any case, the question is how to do cross-wiki joins properly instead of
emulating them with temporary variables, which what I have suggested may be
how one would do it properly, when it works at least //in the foreseeable
future//. (Yes, changing is a possibility but it’s not currently
foreseeable whether or when it will happen.)
[1]
https://phabricator.wikimedia.org/T76466
Zhuyifei1999
On Thu, Jan 18, 2018 at 9:39 AM Brad Jorsch (Anomie) <bjorsch(a)wikimedia.org>
wrote:
On Wed, Jan 17, 2018 at 5:50 PM, YiFei
<zhuyifei1999(a)gmail.com> wrote:
SELECT ... FROM
`<database>`.`<table>`, like in
https://quarry.wmflabs.org/query/24212. This should work in the
foreseeable future, during which all the replica databases are accessible
on the same server.
This is bad advice. Just last week[1] one of our DBAs warned this list
that that ability is not guaranteed or supported, and changing that is
indeed a possibility.
[1]:
https://lists.wikimedia.org/pipermail/cloud/2018-January/000169.html
--
Brad Jorsch (Anomie)
Senior Software Engineer
Wikimedia Foundation
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