This is a potentially breaking change in a very delicate area. However,
examining the code path for writes, I don't see any benefit to opening a
second db connection for them. If the write throws an exception,
commitDb will retry it with a new db connection.
A potential benefit to not opening a second db connection, beyond using
less resources, is it just might avoid problems in WSL with sqlite that
I have hypothesized are caused by multiple db connections.
Commit 5f9eff3f32 explains why it needs to
shut down the db connection to force the database to be updated on disk:
When closeDb does not get called, garbage collection of DbHandle may not
give the workterThread time to cleanly shut down before git-annex exits,
resulting in a recently written change not reaching disk.
After commit f4bdecc4ec, there is no
longer any distinction between SingleWriter and MultiWriter's handling
of read after write.
Databases that were SingleWriter still have lock files that are used to
prevent multiple writers.
This does make writing to such databases a bit more expensive,
because the MultiWriter code path that is now used opens a second db
connection in order to write to them.
This removes a messy caveat that was easy to forget and caused at least one
bug. The price paid is that, after a write to a MultiWriter db, it has to
close the db connection that it had been using to read, and open a new
connection. So it might be a little bit slower. But, writes are usually
batched together, so there's often only a single write, and so there should
not be much of a slowdown. Notice that SingleWriter already closed the db
connection after a write, so paid the same overhead.
This is the second try at fixing a bug: git-annex get when run as the first
git-annex command in a new repo did not populate all unlocked files.
(Reversion in version 8.20210621)
Sponsored-by: Boyd Stephen Smith Jr. on Patreon
