To improve lantency, will ‘CONFIG SET activerehashing no‘’ work？

[ericzh...@gmail.com]

Hello,

I use datadog to monitor our redis server , found the latency of master redis server is over 400 microsecond, I think it is high latency.

To improve it , I want to set paramater of config "activerehashing " to no.

As I found following content on internet.

##activerehashing

The second configuration directive we'll examine is activerehashing. In activerehashing, the main Redis hash table, which links the main keys to values, is rehashed once per 100 milliseconds if this directive is set to yes. This rehashing process releases the deleted keys' memory for use by the operating system, with minimal impact on client connections as the activehashing occurs during downtime. As recommended in the redis.conf comments, activerehashing should be set to no if you have hard latency requirements, or if the Redis server needs to support a high level of concurrent clients that could be delayed during active rehashing.

Our redis server version is 2.8, 

I use 'config get activerehashing' and could get the parameter.

But when I tried 'config set activerehashing no', it failed and pop error like following:

(error) ERR Unsupported CONFIG parameter: activerehashing

Anyone could help me out?

Thanks and regards!

Eric

[Itamar Haber]

Hello Eric,

I tried reproducing this behavior with v2.8.24 and couldn't - setting `activerehashing` to 'yes' succeeds.

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[hva...@gmail.com]

I don't think 400 microseconds (0.0004 seconds) is slow.  400 milliseconds (0.4 seconds) would be slow.  And the source of latency could be any number of things, especially if Redis is on a different machine than the client, and most especially if the Redis machine and/or the client machine is virtualized.

For the CONFIG SET command error, here's a snippet from the 00-RELEASENOTES file from a v2.8.x release:

--[ Redis 2.8.20 ] Release date: 5 May 2015
...
* [FIX] Config: missing activerehashing option support in CONFIG SET added.
        (Salvatore Sanfilippo, thx to Bill Anderson)

You must have a version older than v2.8.20.