virtuoso-t constantly segfaulting

[Duncan]

Thomas Tanghus posted on Thu, 30 Jan 2014 18:22:16 +0100 as excerpted:

>> You could try akonadictl fsck
> 
> I did not know akonadictl had that option! Will try it as soon as I get
> back.
> 
> I now see that it also has a 'vacuum' option, but the help text just
> says "Vacuum internal storage". Do you have any idea what it does?

Active databases (and filesystems, which work similarly) typically create 
and delete a lot of records/files.  Akonadi deals with messaging, so 
consider email and IM messages as they come in, with a lot of them being 
spam and thus often deleted.  But for performance reasons most databases 
and filesystems don't normally entirely wipe all those deleted records 
(files) at the time of deletion; they simply mark them as deleted in 
their index(s) somewhere and continue.

While filesystems will sometimes try to reuse the space for a new file 
later, leading to file and empty-space fragmentation both, databases 
normally append new records at the end, thereby becoming larger and 
larger over time but keeping whole records together with only empty-space 
fragmentation.

Vacuuming a database is conceptually similar to defragging a filesystem.  
In theory, neither one fix errors, but they consolidate data and 
freespace, thereby making access more efficient and shrinking the 
allocated space back down to the space actually being used for storage, 
"vacuuming" up all the little left-over bits of free-space and either 
shrinking the database size (reducing the size of the database file. 
often shrinking it by half or more on an active database with lots of 
deletions) or simply consolidating filesystem free-space, so new files 
will be created in one larger extent instead of perhaps hundreds or 
thousands of tiny extents whereever the filesystem can find the space.

Some databases and filesystems have their own automated vacuum/defrag 
process, while others only do it manually using vacuum/defrag or if you 
create a new one and copy everything over, but most mature filesystems 
and databases, even the ones that normally handle it automatically, have 
a tool vacuum/defrag manually as well, if necessary.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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