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Redis timer interrupt frequency configurable as REDIS_HZ.

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Redis uses a function called serverCron() that is very similar to the
timer interrupt of an operating system. This function is used to handle
a number of asynchronous things, like active expired keys collection,
clients timeouts, update of statistics, things related to the cluster
and replication, triggering of BGSAVE and AOF rewrite process, and so
forth.

In the past the timer was called 1 time per second. At some point it was
raised to 10 times per second, but it still was fixed and could not be
changed even at compile time, because different functions called from
serverCron() assumed a given fixed frequency.

This commmit makes the frequency configurable, so that it is simpler to
pick a good tradeoff between overhead of this function (that is usually
very small) and the responsiveness of Redis during a few critical
circumstances where a lot of work is done inside the timer.

An example of such a critical condition is mass-expire of a lot of keys
in the same second. Up to a given percentage of CPU time is used to
perform expired keys collection per expire cylce. Now changing the
REDIS_HZ macro it is possible to do less work but more times per second
in order to block the server for less time.

If this patch will work well in our tests it will enter Redis 2.6-final.
This commit is contained in:
antirez
2012-05-13 16:40:29 +02:00
parent f333788fbc
commit 9434349236
2 changed files with 56 additions and 20 deletions
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3
src/redis.h
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@ -38,12 +38,13 @@
#define REDIS_ERR -1
/* Static server configuration */
#define REDIS_HZ 10 /* Time interrupt calls/sec. */
#define REDIS_SERVERPORT 6379 /* TCP port */
#define REDIS_MAXIDLETIME 0 /* default client timeout: infinite */
#define REDIS_DEFAULT_DBNUM 16
#define REDIS_CONFIGLINE_MAX 1024
#define REDIS_EXPIRELOOKUPS_PER_CRON 10 /* lookup 10 expires per loop */
#define REDIS_EXPIRELOOKUPS_TIME_LIMIT 25 /* Time limit in milliseconds */
#define REDIS_EXPIRELOOKUPS_TIME_PERC 25 /* CPU max % for keys collection */
#define REDIS_MAX_WRITE_PER_EVENT (1024*64)
#define REDIS_SHARED_SELECT_CMDS 10
#define REDIS_SHARED_INTEGERS 10000