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Re: Fascinating difference between FSFS and BDB.

From: <kfogel_at_collab.net>
Date: 2005-01-14 17:01:52 CET

Branko Čibej <brane@xbc.nu> writes:
> kfogel@collab.net wrote:
> >So don't ask me why, I got it into my head to try this:
> >
> > #!/bin/sh
> > TYPE=you_must_set_this_to_either_fsfs_or_bdb
> > # TYPE=fsfs
> > # TYPE=bdb
> > URL=file://`pwd`/repos/
> > rm -rf repos wc
> > svnadmin create --fs-type=${TYPE} repos
> > svn co ${URL} wc
> > svn propset svn:externals "wc ${URL}" wc
> > svn ci -m "Set recursive externals property." wc
> > rm -rf wc
> > echo "Begin infinite loop..."
> > svn co ${URL} wc
> > # You'll never see this next line.
> > echo "End infinite loop."
> >
> >Here's the interesting thing:
> >
> >With TYPE=fsfs, it runs forever. But with TYPE=bdb, it stops at a
> >certain point -- it seems the database hangs, though I haven't
> >investigated deeply. Too many simultaneous accessors? I don't know.
> >As I'm working on something else right now, I thought I'd post this.
> Probably ran out of locks.

Actually, open file descriptors turns out to be the culprit.

I patched the script to increase lock parameters right after running
'svnadmin create':

   # Fix up DB_CONFIG
   sed -e's/set_lk_max_locks 2000/set_lk_max_locks 20000/' \
      repos/db/DB_CONFIG > repos/db/new.DB_CONFIG
   mv repos/db/new.DB_CONFIG repos/db/DB_CONFIG
   sed -e's/set_lk_max_lockers 2000/set_lk_max_lockers 20000/' \
      repos/db/DB_CONFIG > repos/db/new.DB_CONFIG
   mv repos/db/new.DB_CONFIG repos/db/DB_CONFIG
   sed -e's/set_lk_max_objects 2000/set_lk_max_objects 20000/' \
      repos/db/DB_CONFIG > repos/db/new.DB_CONFIG
   mv repos/db/new.DB_CONFIG repos/db/DB_CONFIG

But when I ran it again, it got exactly as far as it did before. This
time I didn't kill it when it hung, I just waited. Eventually, I got

   $ ./repro.sh
   Fetching external item into 'wc/wc/wc/wc/wc/wc/wc/wc/wc/wc/wc/wc/wc/\
   subversion/libsvn_ra_local/ra_plugin.c:228: (apr_err=180001)
   svn: Unable to open an ra_local session to URL
   subversion/libsvn_ra_local/split_url.c:129: (apr_err=180001)
   svn: Unable to open repository 'file:///home/kfogel/src/subversion/a/repos'
   subversion/libsvn_fs_base/bdb/bdb-err.c:74: (apr_err=160029)
   svn: Berkeley DB error while opening 'copies' table for filesystem \
   Too many open files
   ./doit.sh: line 32: 19783 Aborted svn co ${URL} wc
   End infinite loop.

Over file://, that makes sense.

I tried the same recipe using http://, and the recursion went much
deeper (I eventually killed it, before it brought down my box). We
could "fix" the file:// implementation, but frankly I don't think it's
worth the trouble. Multi-user file:// is probably extremely rare;
multi-user file:// with many externals even rarer.


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Received on Fri Jan 14 17:10:53 2005

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