Wednesday, April 09, 2014

Slow process core dump

Solaris limits rate at which a process core dump is generated. There are two tunables with default values: core_delay_usec=10000 core_chunk=32 (in pages). This essentially means that process core dump is limited to 100 writes of 128KB per second (32x 4k pages on x86) which is an eqivalen of 12.5MB/s - for large processes this will take quite a long time.

I set core_chunk=128 and core_delay_usec=0 via mdb which increased the core dump write rate from 12.5MB/s to about 300-600MB/s.

Long core dump generations can cause issues like delay in restarting a service in SMF. But then making it too fast might overwhelm OS and impact other running processes there. Still, I think the defaults are probably too conservative.

update: I just noticed that this has been fixed in Illumos, see

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