Tuning Global Cache - Expert Oracle RAC Performance Diagnostics and Tuning - page 434

GV$LIBRARYCACHE
The view contains statistics showing library cache performance and activities. When looking at RAC from each
individual instance in the cluster, the RELOADS and INVALIDATIONS columns should be monitored. RELOADS indicates
the number of times the objects had to be reloaded into the library cache due to one or more of the following reasons:

• Objects aging out of the library cache.

• Objects being flushed out of library cache because there is insufficient memory to hold the

objects for long periods of time.

Because reloads are due to objects being flushed out, increasing the size of the shared pool should help.
INVALIDATIONS occur when the objects become invalid because the underlying dependent objects may have been
modified. Invalidations cause the objects to be reparsed once the underlying dependent objects have become valid.
In a RAC environment, the columns of importance are DLM_LOCK_REQUESTS , DLM_PIN_REQUESTS , DLM_PIN_RELEASES ,
and DLM_INVALIDATIONS . These columns are populated due to activity across instances in the cluster when access to
library cache objects must be synchronized with other instances in the cluster. The distributed lock manager (DLM)
in a RAC environment:

SQL> DESC V$LIBRARYCACHE
Name Null? Type
---------------------------- -------- ---------------
NAMESPACE VARCHAR2(64)
GETS NUMBER
GETHITS NUMBER
GETHITRATIO NUMBER
PINS NUMBER
PINHITS NUMBER
PINHITRATIO NUMBER
RELOADS NUMBER
INVALIDATIONS NUMBER
DLM_LOCK_REQUESTS NUMBER
DLM_PIN_REQUESTS NUMBER
DLM_PIN_RELEASES NUMBER
DLM_INVALIDATION_REQUESTS NUMBER
DLM_INVALIDATIONS NUMBER

Script: MVRACPDnTap_dlmlibcache.sql
SELECT inst_id INT,
namespace,
dlm_lock_requests DLREQ,
dlm_pin_requests DPREQ,
dlm_pin_releases DPREL,
dlm_invalidation_requests DINVREQ,
dlm_invalidations DINV
FROM gv$librarycache
ORDER BY inst_id;