Re: Atomic Compare and Swap

[Tim Lossen]

no, but you can easily implement it in lua:

http://redis.io/commands/eval

(each lua script runs atomically, like other redis commands)


On 2012-11-22, at 04:10 , Ritesh Tijoriwala wrote:

> Is there a way to do Atomic Compare and Swap in Redis? Without this, I am not sure how to avoid the extra roundtrip to server which GETs the value and then client does the check.
>
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[Salvatore Sanfilippo]

Well actually WATCH is Redis's (more generic) CAS.

Cheers,
Salvatore

Salvatore 'antirez' Sanfilippo
open source developer - VMware
http://invece.org

Beauty is more important in computing than anywhere else in technology
because software is so complicated. Beauty is the ultimate defence
against complexity.
— David Gelernter

[Ritesh Tijoriwala]

Hi Salvatore,

I am currently using WATCH. However, I have to do an extra GET to compare the values and this forces extra deserialization on client side and one complete roundtrip. For complex objects/values, this can be quite expensive. Is there no way to avoid this?

Thanks for help.

Regards,

Ritesh

[Salvatore Sanfilippo]

Hey, I'm not sure why another GET is required.

Memcached's CAS:

GET key ....
CAS key ....

Redis's WATCH:

WATCH key
GET key
MULTI
SET key ...
EXEC

There is just one get operation in both cases.

However you can use Lua script if you want to improve in the side of
number of commands to send to the server, but note that the first two
and the last three commands can be sent in two separate pipelines so
you pay latency only two times, like in the GET/CAS example.

Cheers,
Salvatore

> https://groups.google.com/d/msg/redis-db/-/b4cthm6KPbIJ.