[darcs-devel] [issue1477] darcs show contents --match 'hash X' is slow

[Zooko]

Zooko <zooko at zooko.com> added the comment:

> So fixing this would only really matter for the case where users
specifically decide to run the source browser on an older version of a
file or directory.

Just to be clear this is a common case. If you want to browse the most
recent version of the source you can just use your text editor on your
local repo, but if you want to browse an older version you need more
tool support. We often browse older versions in the Tahoe-LAFS
development process.

Another problem is that trac locks the entire database while invoking
trac-darcs. So if any user clicks on "annotate" then all users get a
timeout from the entire web site http://allmydata.org/trac/tahoe-lafs
until the "darcs annotate" completes.

Now that's clearly something that could be improved by trac itself -- if
it knew which queries to the revision control plugin were side-effect
free then it could leave the database unlocked when issuing those
commands. Then other users would not be blocked and as long as the
revision control tool was concurrency-safe for multiple simultaneous
read queries and at most one write command nothing bad would happen.

However, it would be really nice if darcs were so fast that it was
usuable for this use case even when trac locks the database for all queries.

There was some more discussion on the mailing list:
http://lists.osuosl.org/pipermail/darcs-users/2010-February/023034.html

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