Tons of I/O operations caused by NullMetadata

[luxemate]

While troubleshooting my production server performance I found out that metadata library is creating a lot of tmp files and renaming to the same name on every request, as there is no property "name" in NullMetadata class (it serializes to an empty class).

Debug information from FileCache::putClassMetadataInCache:

Example of operations from fatrace, that are made on every request:

apache2(1048): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheDIwGQx
apache2(1048): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheDIwGQx
apache2(1048): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheDIwGQx
apache2(1048): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachevRV94h
apache2(1048): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(1048): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(2950): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheAggRB7
apache2(2950): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheAggRB7
apache2(2950): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheAggRB7
apache2(2950): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheAggRB7
apache2(2950): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheAggRB7
apache2(2950): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheNwjvdS
apache2(2950): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheNwjvdS
apache2(2950): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(2950): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(983): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachecxFAVB
apache2(983): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachecxFAVB
apache2(983): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachecxFAVB
apache2(983): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachewGC6Tm
apache2(983): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachewGC6Tm
apache2(983): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachewGC6Tm
apache2(2944): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheSVFyEy
apache2(2944): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheSVFyEy
apache2(2944): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheSVFyEy
apache2(2944): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheSVFyEy
apache2(2944): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cacheDuL8Zj
apache2(2944): CWO /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(2944): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/.cache.php
apache2(2983): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachelktGRx
apache2(2983): CW /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachelktGRx
apache2(2983): O /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachelktGRx
apache2(2983): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachelktGRx
apache2(2983): W /home/luxemate/www/gamesite/app/cache/prod/jms_diextra/metadata/metadata-cachelktGRx

[staabm]

this might be the reson for #44

[roberto-mansfield]

I've found the same issue debugging an issue with the creation of cache files. My composer.lock files says I'm using v1.5.0. In Metadata/Cache/FileCache.php:

public function putClassMetadataInCache(ClassMetadata $metadata)
{
    $path = $this->dir.'/'.strtr($metadata->name, '\\', '-').'.cache.php';

But if there are no annotations, then $metadata is an instance of NullMetadata and then $path points to ".cache.php". Later, when we try to reload the cache file, the "correct" name of the cache file is checked, not found, and so the code tries to generate the same cache file again. So for files with no annotations, you lose the benefit of the cache plus take a hit re-generating the "null" cache files each time.
(FYI: In our production environment, we generate our cache files as read-only which are generated when we deploy updates to our code. That is the context where I ran across this issue.)

[luxemate]

Thanks for the fix, @adrienbrault!