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Re: in-memory-cache TODO

From: Blair Zajac <blair_at_orcaware.com>
Date: Thu, 03 Apr 2008 20:19:09 -0700

David Glasser wrote:
> On Thu, Apr 3, 2008 at 5:22 PM, David Glasser <glasser_at_davidglasser.net> wrote:
>> The in-memory-cache branch is nearing completion. It unifies various
>> caches found in FSFS behind a simple API, and allows the caches to be
>> implemented either in process as hashes or with memcached. If you use
>> memcached (which is enabled in a new fsfs.conf file), caches can live
>> longer than the lifetime of a single svn_fs_t.
>>
>> Remaining TODO:
>> - Move the code which makes an apr_memcache_t based on an
>> svn_config_t to libsvn_subr from FSFS, and use it in the C test.
>> - Build system issues (mostly done by a cache I have from dchristian).
>> - Add --memcache options to the test suite.
>> - Actually run a real benchmark.
>> - Document the fact that all errors communicating with memcached are
>> fail-stop. This is a problem that should be solved with a better svn
>> logging infrastructure, which we ought to get before 1.6 anyway (it's
>> a high priority for my team).
>
> Also make sure that we never pass keys or values that are too big to memcache.

The key can be at most 250 bytes long and in the default memcached configuration
(without recompiling) values 1 Mbyte large.

For keys, if they are longer than 250 bytes, I replace the middle N bytes with a
md5 hex hash of the removed bytes so the key still fits. I know in my app, we
will have paths longer then 250 bytes long, so having this would be nice.

I would be surprised if there's any data that would go over a megabyte. I only
ran into this limitation when I serialized the results of svn_fs_dir_entries()
for a directory with 17,000 entries where each entry had 12 svn properties on
each it. Using gzip compression got 90% compression rates on this data.

Blair

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Received on 2008-04-04 07:53:40 CEST

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