Re: [rdiff-backup-users] KeyError exception

[Austin Clements]

Quoth David on Sep 08 at  9:56 am:
> On 9/7/07, Austin Clements <address@hidden> wrote:
> > I recently changed my configuration for rdiff-backup 1.1.14 and have
> > started getting the following KeyError exception during the backup
> > process (the verbosity level 5 log can be found at the end).
> 
> 2) Create the smallest possible test case that has this problem and
> post details of your setup.

After a great deal of pain and suffering, I've managed to reduce this
problem to an easily reproducible test case.  Put 1999 files or more
in a directory and try to back that up, using a remote schema for both
the source and the destination.  Below is a script that will do the
whole process.


More specifically, (Globals.pipeline_max_length*4-1) is the cut off.
This formula is based on DestinationStruct.set_rorp_cache, which
initializes the CacheCollatedPostProcess.  I still really don't
understand what's going on here, but it has something to do with the
order that the CacheCollatedPostProcess cache is traversed on the
destination rdiff-backup server when the source is also an
rdiff-backup server.

I generated some simple traces of calls to important methods in the
cache and it looks like the order of traversal versus the order in
which methods like get_mirror_rorp are called on the destination is
radically different depending on whether or not the source uses a
remote schema.  I'm not sure, but I think each file in the cache only
gets examined once in the correct case (an index is retrieved from the
cache, then a bunch of methods are called to get more information
about it from the cache, then that index is never looked at again).
In the broken case with a source server, I think the cache is iterated
through once, and _then_ asked for information about the indexes that
were retrieved from it.  Thus, if the first traversal fills up the
cache and causes something to be evicted (ie, if there are 1999 files
or more), the "second" traversal won't be able to retrieve the
additional information and will raise a KeyError.

I'll keep poking at it, but at this point I'm in way, way over my head
on the details of how rdiff-backup works, so it's not likely I'll get
much further on my own.


#!/bin/bash

# Cause rdiff-backup to throw a KeyError

set -e

mkdir /tmp/lotsoffiles
for (( N=0 ; N < 500*4-1 ; N++ )); do
    touch /tmp/lotsoffiles/`printf '%04d\n' $N`
done

rdiff-backup \
    --terminal-verbosity 5 \
    --include /tmp/lotsoffiles \
    --exclude / \
    localhost::/ localhost::/tmp/lotsoffiles-backup

> 5) Provide your kernel version and details of the source and dest
> filesystems (type, any mountpoints involved in the backup).

Source:
  Kernel 2.6.18, Mostly Reiser (/) with a small dash of ext3 (/boot)

Destination:
  Kernel 2.6.21, Reiser mounted via a crypsetup mapper of a USB drive

I ran my above test script on my source machine (and it didn't include
/boot, so it was just Reiser).

> David.

-- 
Austin Clements                                          MIT/'06/CSAIL
address@hidden                         http://web.mit.edu/~amdragon/
       Somewhere in the dream we call reality you will find me,
              searching for the reality we call dreams.