[MediaWiki-l] [Cargo] Duplicate Cargo Rows
edward.hoo at gmail.com
Sun Dec 13 21:14:15 UTC 2015
I went over the code and noticed that DB_SLAVE was being used in read-only
queries that are part of update processes. I do not know if this is what
generated the issues I'm experiencing (I'm not running replication).
However, it could generate race conditions in a replicated environment as
the slave would not always have the most current information. Therefore I
updated the calls to DB_MASTER for the functions that seemed to be called
as part of an update/delete/insert sequence. That left only one or two
instances using DB_SLAVE. So I updated all calls to DB_MASTER for good
measure -- in case I had missed something.
I will run it like this for a while and see if we get more duplicate
entries in the cargo tables.
On Sun, Dec 13, 2015 at 8:39 AM, Yaron Koren <yaron at wikiworks.com> wrote:
> Yes, it probably is due to a race condition.
> Hopefully, there's a better solution than using unbuffered queries - if
> that is a solution.
> On Sun, Dec 13, 2015 at 12:51 AM, Ed <edward.hoo at gmail.com> wrote:
> > Hi,
> > The duplicate rows seem to happen as a result of a race condition when
> > new record has been queued and somewhere in the process we reedit or
> > regenerate and queue a second one.
> > I'm not sure if it is buffering, using multiple connections, something
> > else.
> > I was going to mess around with the DBO_NOBUFFER setting but the comments
> > in "includes/db/Database.php" are a bit ominous:
> > * Unbuffered queries are very troublesome in MySQL:
> > *
> > * - If another query is executed while the first query is
> > read
> > * out, the first query is killed. This means you can't call
> > normal
> > * MediaWiki functions while you are reading an unbuffered
> > query result
> > * from a normal wfGetDB() connection.
> > *
> > * - Unbuffered queries cause the MySQL server to use large
> > amounts of
> > * memory and to hold broad locks which block other queries.
> > Thoughts?
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