Instance hang with very high wait on 'cursor: mutex S' (Doc ID 1274320.1)

Last updated on JUNE 03, 2015

Applies to:

Oracle Database - Enterprise Edition - Version 11.1.0.6 and later
Information in this document applies to any platform.

Symptoms

2 node RAC, intermittently instance is slow then go into 'hang' status without accepting any new connections. There is very high wait of 'cursor: mutex S'.

AWR report during slow/hanging period shows:

Top 5 Timed Foreground Events

Event                     Waits     Time(s) Avg wait (ms) % DB time    Wait Class
cursor: mutex S   5,895,761   19,387            3       32.29     Concurrency
DB CPU                  16,926                                    28.19
library cache lock 122,326      9,803            80     16.33 Concurrency
db file sequential read 524,864  1,332          3       2.22     User I/O
enq: TX - row lock contention  7     380   54317      0.63 Application

Cause

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