Gentlemen, it occurred to me that under close examination one finds
that when making a backup of one's wiki's database, some of the tables
dumped have various degrees of temporariness, and thus though needing
to be present in a proper dump, could perhaps be emptied of their
values, saving much space in the SQL.bz2 etc. file produced.
Looking at the mysqldump man page, one finds no perfect options to do
so, so instead makes one's own script:
$ mysqldump my_database|
perl -nwle 'BEGIN{$dontdump="wiki_(objectcache|searchindex)"}
s/(^-- )(Dumping data for table `$dontdump`$)/$1NOT $2/;
next if /^LOCK TABLES `$dontdump` WRITE;$/../^UNLOCK TABLES;$/;
print;'
Though not myself daring to make any recommendations on
http://www.mediawiki.org/wiki/Manual:Backing_up_a_wiki#Tables
I am still curious which tables can be emptied always,
which can be emptied if one is willing to remember to run a
maintenance script to resurrect their contents, etc.