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Re: Inconsistencies in FSFS cache-* options

From: Stefan Fuhrmann <stefan2_at_apache.org>
Date: Tue, 18 Apr 2017 16:54:58 +0200

On 16.03.2017 15:08, Julian Foad wrote:
> Stefan2 et al.:
>
> Nodeprops caching is new in 1.10. This caused me to have a look at the
> code for enabling it, and I noticed the following in FSFS (and the
> same in FSX).
>
> In subversion/libsvn_fs_fs/caching.c_at_1787000, around line 100:
> > /* don't cache text deltas by default.
>
> Wrong: the default was changed to TRUE in r1517479, and this new
> default is contrary to the reasoning given in this comment.
>
> > * Once we reconstructed the fulltexts from the deltas,
> > * these deltas are rarely re-used. Therefore, only tools
> > * like svnadmin will activate this to speed up operations
> > * dump and verify.

Yup, that comment is outdated. Fixed in r1791793.

> > */
> > *cache_txdeltas
> > = svn_hash__get_bool(fs->config,
> > SVN_FS_CONFIG_FSFS_CACHE_DELTAS,
> > TRUE);
> [...]
> > /* by default, cache nodeprops: this will match pre-1.10
> > * behavior where node properties caching was controlled
> > * by SVN_FS_CONFIG_FSFS_CACHE_FULLTEXTS configuration option.
>
> The default of TRUE doesn't match that behaviour, does it? To do so,
> should the last argument (below) be "*cache_txdeltas" instead of "TRUE"?

In r1791793, I tried to make Ivan's intention more clear.
>
> > */
> > *cache_nodeprops
> > = svn_hash__get_bool(fs->config,
> > SVN_FS_CONFIG_FSFS_CACHE_NODEPROPS,
> > TRUE);
>
> Also, the handling of these flags in mod_dav_svn (around line 990) is
> odd:
>
>> svn_boolean_t
>> dav_svn__get_txdelta_cache_flag(request_rec *r)
>> {
>> dir_conf_t *conf;
>>
>> conf = ap_get_module_config(r->per_dir_config, &dav_svn_module);
>>
>> /* txdelta caching is enabled by default. */
>> return get_conf_flag(conf->txdelta_cache, TRUE);
>> }
>>
>>
>> svn_boolean_t
>> dav_svn__get_fulltext_cache_flag(request_rec *r)
>> {
>> dir_conf_t *conf;
>>
>> conf = ap_get_module_config(r->per_dir_config, &dav_svn_module);
>> return conf->fulltext_cache == CONF_FLAG_ON;
>
> This construction ("==ON") means the default here is OFF, which is the
> opposite of the default that FSFS would apply if we didn't pass it any
> value for this flag.
>
>> }
>>
>>
>> svn_boolean_t
>> dav_svn__get_revprop_cache_flag(request_rec *r)
>> {
>> dir_conf_t *conf;
>>
>> conf = ap_get_module_config(r->per_dir_config, &dav_svn_module);
>> return conf->revprop_cache == CONF_FLAG_ON;
>> }
>>
>> svn_boolean_t
>> dav_svn__get_nodeprop_cache_flag(request_rec *r)
>> {
>> dir_conf_t *conf;
>>
>> conf = ap_get_module_config(r->per_dir_config, &dav_svn_module);
>> /* node properties caching is enabled by default. */
>> return get_conf_flag(conf->nodeprop_cache, FALSE);
>
> The code here uses a default value of "FALSE", which is different from
> the fsfs.conf default value (see above), and doesn't match the comment
> here.

Yes, the whole section is quite inconsistent. r1791794 should fix this.

Thanks for the review!

-- Stefan^2.
Received on 2017-04-18 16:55:17 CEST

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