We have environment of multi-master and slave replication . 

master1 < =====> master 2 

     |                              |

     |                              |

     Slave 1                   Slave 1 &

     & slave 2                  slave 2

Now we are facing issue in all slaves, where replication from master is very slow. All slaves are single threaded. 

We are seeing High RECQ and sometimes server goes unavailable, untill we restart the slapd service. 

tcp 757967 0 ****:36340 *****:636 ESTABLISHED 22160/slapd

Could someone tell me, what kind of tuning we can perform?. If we make multi threaded, it will not have much performance. 

Kindly help .. Production servers are having this issue. Other system configuration like (Memory, load, disk) everything looks okay. 

I checked this kernel parameters as well. 

net.core.rmem_max = 4194304
net.ipv4.tcp_rmem = 4096 65536 4194304

Regards

K.Keerthiga