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 (TxEventQs) 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