Memcached
ArielGlenn (Talk | contribs) (→Editing mc.php) |
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Note that all servers that are up will return <tt>incr: 100 get: 100</tt> and servers that are down will return <tt>incr: 0 get: 0</tt>. | Note that all servers that are up will return <tt>incr: 100 get: 100</tt> and servers that are down will return <tt>incr: 0 get: 0</tt>. | ||
| − | = Editing mc.php = | + | == Editing mc.php == |
Please note what the file says, the order and format is '''very important.''' Make sure you add servers to the correct ***DOWN*** or ***SPARE*** sections, removing the slot number and replacing it with XX. If you move a server into the memcached pool, ensure you remove the XX and put in the correct number. | Please note what the file says, the order and format is '''very important.''' Make sure you add servers to the correct ***DOWN*** or ***SPARE*** sections, removing the slot number and replacing it with XX. If you move a server into the memcached pool, ensure you remove the XX and put in the correct number. | ||
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<tt>sync-file mc.php ''enter the reason for updates'' </tt> | <tt>sync-file mc.php ''enter the reason for updates'' </tt> | ||
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| + | === Adding Servers to the Memcache pool === | ||
| + | |||
| + | Currently, this is a very serious undertaking, as even adding a single server to the total number of servers causes the need for all memcached servers to completely rebuild their cache. Simple explination by Domas is crc32(key) % modulus. That is on our side, not memcached, and thus is the issue. | ||
| + | |||
| + | We are not sure the impact, only that it possibly may not lat long, but we have no real info on this. | ||
Revision as of 18:42, 8 September 2010
The memcached master php file is located in:
/home/wikipedia/common/wmf-deployment/wmf-config/mc.php
You can install a memcached server with:
apt-get install memcached
Be certain you start memcached after install. The installer states it is starting it, but it lies.
You can test the servers to see which memcached are functioning and which are not with the following:
cd /home/w/common/wmf-deployment/maintenance; php mctest.php
Note that all servers that are up will return incr: 100 get: 100 and servers that are down will return incr: 0 get: 0.
Editing mc.php
Please note what the file says, the order and format is very important. Make sure you add servers to the correct ***DOWN*** or ***SPARE*** sections, removing the slot number and replacing it with XX. If you move a server into the memcached pool, ensure you remove the XX and put in the correct number.
If you want to add a server from the spare list to the active list, please test it first. You can run
/home/wikipedia/common/wmf-deployment/maintenance/mctest.php enwiki ip-address-here:11000
(it runs on a nonstandard port). As above, servers that are up will return incr: 100 get: 100 and servers that are down will return incr: 0 get: 0.
If you fix a memcached server and it is not immediately needed to go into rotation, be sure to move it from DOWN to SPARE.
Once you finish updating the file, you need to sync it out with the following:
sync-file mc.php enter the reason for updates
Adding Servers to the Memcache pool
Currently, this is a very serious undertaking, as even adding a single server to the total number of servers causes the need for all memcached servers to completely rebuild their cache. Simple explination by Domas is crc32(key) % modulus. That is on our side, not memcached, and thus is the issue.
We are not sure the impact, only that it possibly may not lat long, but we have no real info on this.
