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Re: BerkeleyDB performance on Linux
David Boreham wrote:
Howard Chu wrote:
I think the difference is so small because the caches were already at
a 99% hit rate; very few requests would actually need to do I/O.
Right, that was my concern. When I tried this (was done on both Linux
I saw performance in the non-100% hit rate case fall significantly.
Hm... Something doesn't sound right here. If the buffer cache is actually
mitigating that effect, that implies that you could allocate more space to
the BDB cache and get the same benefit. (Indeed, looking at the system status
at the end of the test, with 4.2GB in the buffer cache, that tells me that I
should have raised our BDB cache to 4.2GB.) The other side of this is that
using O_DIRECT eliminates the double-buffering that's occurring, so each I/O
that actually needs to be done does one less memcpy.
But again, using O_DIRECT means every I/O is synchronous, so I guess that
might wreak havoc on any queuing optimizations in the fs.
-- Howard Chu
Chief Architect, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc
OpenLDAP Core Team http://www.openldap.org/project/