Oracle 视图 V$AQ_MESSAGE_CACHE_STAT 官方解释，作用，如何使用详细说明

NUM_EVICTED

NUMBER

Number of evicted subshards across all sharded queues

NUM_PREFETCHED

NUMBER

Number of subshards pre-fetched by AQ background process

NUM_UNEVICTION

NUMBER

Number of subshards un-evicted by foreground process (like dequeue process)

NUM_UNCACHED

NUMBER

Number of subshards stored as uncached

NUM_TRACKED

NUMBER

Number of subshards which are actively tracking dequeue rates

NUM_CACHED

NUMBER

Number of subshards stored as cached

MAX_SUBSH_SIZE

NUMBER

Maximum subshard size seen till now, in terms of number of messages per subshard

MIN_SUBSH_SIZE

NUMBER

Minimum subshard size seen till now, in terms of number of messages per subshard

MEAN_SUBSH_SIZE

NUMBER

Mean subshard size seen till now, in terms of number of messages per subshard

AVG_EVICTION_RATE

NUMBER

Average number subshards evicted per second

AVG_LOAD_RATE

NUMBER

Average number of subshards pre-fetched or un-evicted per second

AVG_EVICTION_TIME

NUMBER

Average time taken to evict one subshard (in milliseconds)

AVG_LOAD_TIME

NUMBER

Average time taken to un-evict one subshard (in milliseconds)

AVG_MISS_RATIO

NUMBER

Average ratio of number of foreground un-evictions versus background pre-fetch

AVG_THRASH_RATIO

NUMBER

Average ratio of number of subshard pre-fetched by background without dequeue attempt versus total number of subshards prefetched

MANDATORY_AFF_SWITCH_ATTEMPTS

NUMBER

An affinity switch is a change in dequeue instance for a shard-subscriber pair. A mandatory affinity switch is when there are local enqueues in the queue at the instance but no local dequeues present, so the dequeue affinity is switched to another instance for that shard-subscriber pair. This column shows the number of times mandatory affinity switches were attempted across all instances. Populated at the smallest instance id only.

OPTIONAL_AFF_SWITCH_ATTEMPTS

NUMBER

Optional affinity switches are affinity switches that are not mandatory. Optional affinity switches are done for global load balancing across the Oracle Real Application Clusters (Oracle RAC) database. This column shows the number of times optional affinity switches were attempted across all instances. Populated at the smallest instance id only.

MIN_EVICT_PERCENT

NUMBER

Percentage of streams_pool memory beyond which sharded queue subshard eviction is triggered

LAST_AVG_CACHED_HORIZON

NUMBER

Last average number of cached subshards seen in sharded queue memory manager horizon

LAST_AVG_MEMORY_HORIZON

NUMBER

Last average memory of cached subshards seen in sharded queue memory manager horizon

LAST_AVG_SUBSHARD_HORIZON

NUMBER

Last average number of subshards seen in sharded queue memory manager horizon

LAST_LEEWAY_SHIFT

NUMBER

Internal leeway for memory threshold

AVG_OPTTIME_DRIFT

NUMBER

Average drift of opt_time for all subshards. A drift is defined as a difference between opt_time as set on a subshard and the actual time at which subshard is first dequeueed after prefetch/uneviction.

NUM_THRESHOLD_DRIFT

NUMBER

Number of times drift value has gone over threshold time. A typical threshold time can be horizon_time/2.

MAX_OPT_TIME_DRIFT

NUMBER

Maximum drift till now

MIN_OPT_TIME_DRIFT

NUMBER

Minimum drift till now

AVG_OPT_TIME_ERROR

NUMBER

An opt_time error occurs when a cached subshard is unevicted by a foreground process (instead of being prefetched by the aq background). Thus, opt_time error is the difference between the actual opt_time set for a sharded queue subshard and the absolute time at which foreground unevicts the same subshard. This column represents average time of this error.

MAX_OPT_TIME_ERROR

NUMBER

Maximum opt_time error

MIN_OPT_TIME_ERROR

NUMBER

Minimum opt_time error

NUM_FG_RELOADED

NUMBER

Number of subshards reloaded from disk into message cache by foreground processes

NUM_PRERELOADED

NUMBER

Number of subshards reloaded from disk into message cache in advance by background processes

AVG_RELOAD_TIME

NUMBER

Average time to reload a subshard from disk into message cache (in milliseconds)

CON_ID

NUMBER

The ID of the container to which the data pertains. Possible values include:

• 0: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs.

• 1: This value is used for rows containing data that pertain to only the root

• n: Where n is the applicable container ID for the rows containing data