If a process has two blocking operations, each blocking other (like, I/O and networking), theoretical performance decrease will be 50%. Solution is very easy – convert one operation (quite often the one that blocks less, but I guess it doesn’t matter that much) into a nonblocking one.
Though MySQL has network-write buffer, which provides some async network behavior, it still has to get context switch into a thread to write stuff.
rsync and other file transfer protocols are even worse in this regard. On a regular Linux machine rsync even on gigabit network will keep kernel’s send-queue saturated (it is 128K by default anyway).
How to make MySQL’s or rsync networking snappier? If in ‘netstat’ sendq column is maxed out – just increase kernel buffers, instead of process buffers:
# increase TCP max buffer size net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 # increase Linux autotuning TCP buffer limits # min, default, and max number of bytes to use net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216
This can add additional 10-20% of file transfer throughput (and sendq goes up to 500k – so it seems to be really worth it).
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