8.25 V$AQ_MESSAGE_CACHE_ADVICE

V$AQ_MESSAGE_CACHE_ADVICE shows simulated metrics for a range of potential message cache sizes. This view assists in cache sizing by providing information in the form of metrics as described below.

Note:

AQ sharded queues are deprecated in Oracle Database 21c. Oracle recommends that you instead use Transactional Event Queues (TEQs) for higher throughput and better performance.
Column Datatype Description

SIZE_FOR_ESTIMATE

NUMBER

Cache size for simulation (in megabytes)

SIZE_FACTOR

NUMBER

Size factor with respect to the current cache size

ESTD_SIZE_TYPE

VARCHAR2(9)

Possible values:

  • MINIMUM: This cache size is required to have all dequeues in-memory (no uncached).

  • PREFERRED: This is the smallest message cache size required to eliminate 80% of unevictions that occur with a message cache size of MINIMUM for subscribers who keep up, that is, subscribers whose dequeue rate matches the enqueue rate.

  • MAXIMUM: This cache size is required to have zero evictions.

  • NULL: This is the value in all other cases.

ESTD_CACHED_SUBSHARDS

NUMBER

Estimated number of cached subshards for this size

ESTD_UNCACHED_SUBSHARDS

NUMBER

Estimated number of uncached subshards for this size

ESTD_EVICTIONS

NUMBER

Estimated number of subshards evicted for this size

ESTD_EVICTION_RATE

NUMBER

Estimated number of subshards getting evicted per minute

ESTD_FG_UNEVICTIONS

NUMBER

Estimated number of subshards unevicted by foreground processes

ESTD_FG_UNEVICTION_RATE

NUMBER

Estimated number of subshards getting unevicted by foreground processes

ESTD_BG_UNEVICTIONS

NUMBER

Estimated number of subshards unevicted by background processes

ESTD_BG_UNEVICTION_RATE

NUMBER

Estimated number of subshards getting unevicted by background processes

ESTD_BG_PROCESSES

NUMBER

Estimated number of background processes required for this size

TOTAL_ENQUEUE_RATE

NUMBER

Simulated number of messages being enqueued per second

TOTAL_DEQUEUE_RATE

NUMBER

Simulated number of messages being dequeued per second

AVG_SUBSHARD_SIZE

NUMBER

Simulated average number of messages per cached subshard

AVG_SUBSHARD_MEMORY

NUMBER

Simulated average memory per cached subshard (in megabytes)

AVG_EVICTION_TIME

NUMBER

Simulated average time to evict a cached subshard (in milliseconds)

AVG_UNEVICTION_TIME

NUMBER

Simulated average time to unevict a cached subshard (in milliseconds)

FLAGS

NUMBER

Reserved for internal use

SIMULATION_TIME

NUMBER

Amount of time that was simulated for (in minutes)

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