A threadsafe problem

[Shunbin]

Our project uses a Redis instance as the persistent database(located localhost, AOF enabled, no master/slave, no cluster, version 2.8.24), 

and Tomcat 6 as the application server. They communicates through Jedis(versioin 2.5.1). It published half a year ago, ran smoothly.

However, When the Redis instance became fat(about 10G), an unexpected phenomenon happened. It seemed our redis instance confused 

keys and values at a very low probability. For instance,

set key1, value1

set key2, value2

......

set keyN, valueN

Most of the time, getting keyX returned valueX as expected. But sometimes it returned valueY. It seems a

threadsafe problem. But we use Jedis like this pattern:

private void doRequest(HttpServletRequest req, HttpServletResponse resp) {

Jedis jedis = new Jedis();

try {

//do things

} finally {

jedis.close();

}

}

It should be threadsafe.

Analyzed the server's logs we noticed that all the illegal writes happened when a AOF rewrite triggered. 

At that time a lot of socket read timeout exceptions of Jedis reported. 

Maybe a large latency of redis motivated this threadsafe bug.

We have let no-appendfsync-on-rewrite to yes. Now no such bug occurred, but still unresolved.

[Salvatore Sanfilippo]

Hello, this looks like a problem in your client that shows up in a
time-dependent manner, so happens when Redis happens to be slower.
Redis is single-threaded in regard of processing operations so can't
have this bug.

Cheers,
Salvatore

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--
Salvatore 'antirez' Sanfilippo
open source developer - Redis Labs https://redislabs.com

"If a system is to have conceptual integrity, someone must control the
concepts."
— Fred Brooks, "The Mythical Man-Month", 1975.