TYPO3运行超过1小时后，网站响应时间与memcached不稳定

Question

I have a couple of websites that get very slow (25+ sec response time) at some times. Requests directly after such a slow request are most of the time normally fast (without browser and varnish cache). It happens to any page and I can't reproduce it with a single webserver (and memcached), but I can on a setup with 2 webservers.

In the php5-fpm-www.slowlog I see a lot stack-traces that mostly end in memcache. After flushing memcached the sites are fast again for about 1 hour after which the slow pages occur again.

For my TYPO3 6.2.15 stack I use 3 servers on rackspace: 2 webservers and one NFS server.The webserver have shared memcached(VERSION 1.4.14 (Ubuntu)). The rest of the stack consists of Varnish, Nginx and php5-fmp all running on ubuntu trusty 14.04. For a database I use the rackspace MySql database.

I store the following tables in memcached: cache_hash, cache_pages, cache_pagesection, cache_rootline, extbase_datamapfactory_datamap, extbase_object, extbase_reflection, extbase_typo3dbbackend_tablecolumns, extbase_typo3dbbackend_queries

$GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations'][$tableCache]['backend'] = 'TYPO3\\CMS\\Core\\Cache\\Backend\\MemcachedBackend'; $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations'][$tableCache]['options']['servers'] = $memcachedServers; $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations'][$tableCache]['options']['defaultLifetime'] = 86400;

For now I have switched to filecache, which makes the sites a little bit slower, but with stable response time.

Has anyone experience with this kind of problems and what was your fix?

Answer 1

According to TYPO3 documentation, memcached should not be used for any cache that uses tags.

Because of the mentioned drawbacks, the memcached backend should be used with care or in situations where cache integrity is not important or if a cache has no need to use tags at all. Currently, the memcache backend implements the TaggableBackendInterface, so the implementation does allow tagging, even if it is not advised to used this backend together with heavy tagging.

Also, memcached should be use for caches with predictable size: if the max allowed memory allowed to memcached is reached, memcached will start evicting data.

For those reasons, you should avoid using of memcached for cache_hash, cache_pages and any cache that grows fast and use tags.