Cuirass WAL size issues

[Christopher Baines]

Hey,

I've been chasing some performance issues in the Guix Build Coordinator
and thought that the size of the WAL file was a contributing factor.

I believe SQLite checkpoints the WAL file after transactions commit, if
the WAL is over 1000 pages in size. At least for the Guix Build
Coordinator though, that didn't seem to be working/happening as the WAL
file seemed to just grow and grow.

I think I'm making some progress on that. It seems that if you don't
reset or finalise statements after you're finished with them, bad things
happen. I think one of these bad things is that WAL checkpointing stops
happening. When I got that to happen in the Guix Build Coordinator, I'm
no longer seeing errors when I try and manually run checkpoints now.

Switching focus to Cuirass, I think it's got similar issues. I've pushed
a few commits to this branch [1], the important one being [2] which
rewrites a few procedures to call sqlite-reset when the statement is
finished with, rather than calling it before starting to read from the
statement.

1: https://git.cbaines.net/guix/cuirass/log/?h=sqlite-statement-reset-fixes
2: 
https://git.cbaines.net/guix/cuirass/commit/?h=sqlite-statement-reset-fixes&id=e09bc606f25bad11b39c9fae49139ac03b88697c

If this makes sense, I can spend the time writing some changelog entries
for the commits, and push them. What do you think?

Thanks,

Chris

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