Add batch-lines support to Redis destination

[OverOrion]

This PR adds batch-lines() support for the redis destination driver which increases performance.
Performance improvement is significant (8665U, 32 GiB RAM): [1]

8 workers, no batch-lines() option	8 workers, batch-lines(100)
~ 80k/s	~ 240k/s (peak 450k/s)

The batching is based on the pipelining feature of Redis. We have to count the sent (appended) messages as we must retrieve as many as we sent.

I also tested that when the Redis server goes offline it will reconnect.

[1] I used the following configuration:

source s_local {
        network(
        port(4444)
        max-connections(100)
        log-iw-size(100000)
        log-fetch-limit(1000)
        );
};
destination d_redis {
    redis(
        host("localhost")
        port(6379)
        command("HINCRBY", "hosts", "$HOST", "1")
        workers(8)
        log-fifo-size(100000)
        batch-lines(100)
    );
};

log {
        source(s_local);
        destination(d_redis);
        flags(flow-control);
};

And sent messages via loggen:
./loggen --permanent --rate=10000000 --active-connections 10 -i localhost 4444

Signed-off-by: Parrag Szilárd szilard.parrag@gmail.com

[kira-syslogng]

Build SUCCESS

[Barkodcz]

Nice, thank you!

[MrAnno]

Please add a news file entry about the new options: batch-lines() and batch-timeout().

[kira-syslogng]

Build SUCCESS

[kira-syslogng]

Build SUCCESS

Thank you

[kira-syslogng]

Build FAILURE

[kira-syslogng]

Build SUCCESS

[kira-syslogng]

Build SUCCESS