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Large SQL files are not deltified?

From: Daniel DeLorme <dan-ml_at_dan42.com>
Date: 2007-09-05 11:27:25 CEST

I'm trying to use svn to backup SQL files because I'd like to have the
whole versioned history of the database at my fingertips instead of
having to keep around a big pile of DVDs. Since each successive SQL dump
has relatively few changes I thought this would be perfect for svn. To
make it easier on svn I dumped each table into its own SQL file, ordered
by primary key. Most files are small but the biggest is 63 MB. I
expected the first commit to take a lot of space and subsequent commits
to use only a little space each, but instead I got the opposite!

rev1: initial commit ~2M lines
2,059,337 lines 257,095,356 bytes
-> repo/db/revs/1 is 85,119,507 bytes

rev2: -74,399 +345,127 lines
2,330,075 lines 290,885,872 bytes
-> repo/db/revs/2 is 100,085,702 bytes!

rev3: -27,881 +38,092 lines
2,340,286 lines 292,217,590 bytes
-> repo/db/revs/3 is 154,831,162 bytes!

Can anyone explain to me what is going on? I expected revision 3, with
the smallest changeset, to have the smallest file size in the repository
but instead it's the biggest. Even if I take into account the
skip-deltas[1] algorithm, rev3 should use rev2 as the base delta,
resulting in a small revision file size. I'm very confused.

[1] http://svn.collab.net/repos/svn/trunk/notes/skip-deltas

PS: is there any way to disable the skip-deltas algo? If possible I'd
like to always use N-1 as the base delta because I care more about space
savings for this particular case.

PPS: In an older thread[2] it was suggested to use rdiff-backup for
this, but I'd like to have some of the svn niceties like versioned file

[2] http://subversion.tigris.org/servlets/ReadMsg?list=users&msgNo=48408

Thanks in advance for any information on this behavior,

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Received on Wed Sep 5 11:24:29 2007

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