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Re: [RFC/PATCH] svnadmin: recover/hotcopy erroring out for old FSFS repositories

From: Evgeny Kotkov <evgeny.kotkov_at_visualsvn.com>
Date: Fri, 31 Jan 2014 05:50:32 +0400

> This only affects non-sharded repositories with rev-local IDs,
> i.e. those in SVN 1.4 format. For those, it is writing 3 files
> instead of 2 per rev now.

I assume you are talking about r1560723 [1]. If I read the code correctly...
      if ( (!max_files_per_dir || rev % max_files_per_dir == 0)
          && dst_ffd->format >= SVN_FS_FS__MIN_NO_GLOBAL_IDS_FORMAT)
        SVN_ERR(hotcopy_update_current(&dst_youngest, dst_fs, rev, iterpool));

...hotcopy now checkpoints after every revision for all non-sharded repositories
with FSFS format >= 3. So, checkpointing happens for all FSFS format 1/2
repositories upgraded via 'svnadmin upgrade' (with linear layout), that were
not fsfs-reshard'ed or dump/loaded into a repository with newer format.

I am not aware of how many people reshard or dump/load their old repositories
after upgrade, but I did a quick benchmark for a real-world repository and on my
machine it shows 7x performance degradation with checkpointing enabled. Is it
worth the ability to re-run the backup from a checkpoint upon cancellation?

  # svnrdump http://googletest.googlecode.com/svn/trunk/
  # load the dump into a --compatible-version=1.3 repository
  # upgrade the repository with the most recent svnadmin

  # disable checkpointing, benchmark making 100 hotcopy backups:
  real 0m18.741s
  user 0m2.552s
  sys 0m13.432s

  # now enable checkpointing and repeat the benchmark:
  real 2m5.793s
  user 0m0.836s
  sys 0m34.840s

[1] http://svn.apache.org/viewvc?view=revision&revision=r1560723

Evgeny Kotkov
Received on 2014-01-31 02:51:26 CET

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