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Eliminating the text-base penalty

From: Greg Hudson <ghudson_at_MIT.EDU>
Date: 2002-09-25 07:59:52 CEST

Here's a brain dump on getting rid of the text-base penalty, since
some people expressed interest.

Option 1 is to, given the appropriate checkout option, omit the text
base and instead store a checksum of the working copy file (after
newline and keyword substitution, but with no local modifications).
We can use this checksum to detect whether a working copy file has
changed, if the mod time has budged.

Any operation which needs the text base will have to pull it off the
server if the working copy file has changed.

Option 2 is to implement read-only working copies. The idea here is
that, given the appropriate checkout option, files are checked out
read-only with no text-base. When you want to edit a file, you have
to do an "svn edit filename" to make it read-write; this creates a
text-base (either by pulling it from the repository or by
de-substituting it from the working copy; the latter option doesn't
require the network but would require stashing some notes about what
substitutions we performed on each file). So you only pay a text-base
penalty on files you've chosen to edit.

Read-only working copies have a couple of other applications as well.
One is advisory locking; another is "fast crawl," which I described in

Any major post-1.0 cycles I might have are currently reserved for a
direct-mapping filesystem back end, so I don't expect to put effort
into either of these plans.

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Received on Wed Sep 25 08:09:04 2002

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