Generally speaking objectcache is used as a last resort form of caching if you dont have apcu, memcached, redis, or something else configured.
Truncating the contents of the table will make the next couple of requests to mediawiki slower as some of the cache entries will need to be rebuilt. But it probably wont be horrible as long as you dont do it too often. Id reccomend experimenting during off peak hours so you can see what the performance impact is.
In the long run, I would reccomend installing apcu so that cache stuff is stored there instead of the db.
-- Brian
On Tuesday, February 6, 2018, John Horne john.horne@plymouth.ac.uk wrote:
Hello,
We are running an old version of mediawiki (1.24.2), and have noticed
recently
that overnight we are seeing that the disk utilisation is reaching nearly
100%
for almost an hour. During the night, at different times, we run a
database
backup (mysqldump) and a database check (mysqlcheck). It turns out that
these
are causing the disk usage problem.
In particular the database table 'objectcache' has nearly 500,000 entries. Whilst the table has an expiry date/time field for the records, all but
about
10 of the records have the expiry date set to the year 2038!
Looking at the key names for some of the records they seem to be of the
form:
'SM:resourceloader:filter:minify-css:7:066ff155efe7761cc6472668436b9554'.
My questions are:
- Is it right that 'minify-css' records should have a very long expiry
date
(such that they are basically going to accumulate over time)?
- The mediawiki docs say that it is possible to purge the table as
required
since the records will be recreated. Will this have any effect on someone
who
is using the wiki at the time the table is purged?
Current plans are to modify our backup script to exclude the table, but
include
its 'structure' into the backup file. (Kudos to AmitP's answer at
https://stackoverflow.com/questions/13593148/mysql-dump-exclude-some-table-d...
). In addition, our database check script will perform a table purge
beforehand
if it is safe to do so. (Plans also include updating the mediawiki version!)
Thanks,
John.
-- John Horne | Senior Operations Analyst | Technology and Information
Services
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