Tuning ZFS: performance anomaly with nocacheflush

Good day list,

We are investigating why turning on the ZFS nocacheflush would affect a simple (traditional) import so drastically. With the nocacheflush default (0), we observe normal behavior. With the nocachflush set to 1, we observe each db writer process suddenly having a LWP (Lightweight Process) count in excess of 150 (some up to 175). This caused significant kernel contention and slowed down the import significantly. A truss on dbwr processes shows lots of sleeping and lwp_parking. I was not able to find much relevant information on google or metalink for tags "oracle zfs nocacheflush". Any ideas?

Oracle EE 10.2.0.2 on Solaris 10, hardware is Sun T5240, EMC C3-80 SAN.

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Charles Schultz

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