REDIS_HZ is the frequency our serverCron() function is called with. A more frequent call to this function results into less latency when the server is trying to handle very expansive background operations like mass expires of a lot of keys at the same time. Redis 2.4 used to have an HZ of 10. This was good enough with almost every setup, but the incremental key expiration algorithm was working a bit better under *extreme* pressure when HZ was set to 100 for Redis 2.6. However for most users a latency spike of 30 milliseconds when million of keys are expiring at the same time is acceptable, on the other hand a default HZ of 100 in Redis 2.6 was causing idle instances to use some CPU time compared to Redis 2.4. The CPU usage was in the order of 0.3% for an idle instance, however this is a shame as more energy is consumed by the server, if not important resources. This commit introduces HZ as a runtime parameter, that can be queried by INFO or CONFIG GET, and can be modified with CONFIG SET. At the same time the default frequency is set back to 10. In this way we default to a sane value of 10, but allows users to easily switch to values up to 500 for near real-time applications if needed and if they are willing to pay this small CPU usage penalty.
Two limits are added: 1) Up to SLOWLOG_ENTRY_MAX_ARGV arguments are logged. 2) Up to SLOWLOG_ENTRY_MAX_STRING bytes per argument are logged. 3) slowlog-max-len is set to 128 by default (was 1024). The number of remaining arguments / bytes is logged in the entry so that the user can understand better the nature of the logged command.
After considering the interaction between ability to delcare globals in scripts using the 'global' function, and the complexities related to hanlding replication and AOF in a sane way with globals AND ability to turn protection On and Off, we reconsidered the design. The new design makes clear that there is only one good way to write Redis scripts, that is not using globals. In the rare cases state must be retained across calls a Redis key can be used.
…dis.conf or via CONFIG SET/GET. Also CONFIG SET support added for rdbcompression as well.
This commit introduces support for read only slaves via redis.conf and CONFIG GET/SET commands. Also various semantical fixes are implemented here: 1) MULTI/EXEC with only read commands now work where the server is into a state where writes (or commands increasing memory usage) are not allowed. Before this patch everything inside a transaction would fail in this conditions. 2) Scripts just calling read-only commands will work against read only slaves, when the server is out of memory, or when persistence is into an error condition. Before the patch EVAL always failed in this condition.
…iled (and at least one save point is configured). However people having good monitoring systems may prefer a server that continues to work, since they are notified that there are problems by their monitoring systems. This commit implements the ability to turn the feature on or off via redis.conf and CONFIG SET.
…nf by using a save directive with a single empty string argument, like it happens for CONFIG SET save.
… as replication timeout.