aurora_ccm_status - Amazon Aurora
SyntaxArgumentsReturn typeUsage notesExamples
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aurora_ccm_status

Displays the status of cluster cache manager.

Syntax

aurora_ccm_status()

Arguments

None.

Return type

SETOF record with the following columns:

  • buffers_sent_last_minute – The number of buffers sent to the designated reader in the past minute.

  • buffers_found_last_minute – The number of frequently accessed buffers identified during the past minute.

  • buffers_sent_last_scan – The number of buffers sent to the designated reader during the last complete scan of the buffer cache.

  • buffers_found_last_scan – The number of frequently accessed buffers sent during the last complete scan of the buffer cache. Buffers that are already cached on the designated reader aren't sent.

  • buffers_sent_current_scan – The number of buffers sent during the current scan.

  • buffers_found_current_scan – The number of frequently accessed buffers that were identified in the current scan.

  • current_scan_progress – The number of buffers visited so far during the current scan.

Usage notes

You can use this function to check and monitor the cluster cache management (CCM) feature. This function works only if CCM is active on your Aurora PostgreSQL DB cluster. To use this function you connect to the Write DB instance on your Aurora PostgreSQL DB cluster.

You turn on CCM for an Aurora PostgreSQL DB cluster by setting the apg_ccm_enabled to 1 in the cluster's custom DB cluster parameter group. To learn how, see Configuring cluster cache management.

Cluster cache management is active on an Aurora PostgreSQL DB cluster when the cluster has an Aurora Reader instance configured as follows:

  • The Aurora Reader instance uses same DB instance class type and size as the cluster's Writer instance.

  • The Aurora Reader instance is configured as Tier-0 for the cluster. If the cluster has more than one Reader, this is its only Tier-0 Reader.

Setting more than one Reader to Tier-0 disables CCM. When CCM is disabled, calling this function returns the following error message:

ERROR: Cluster Cache Manager is disabled

You can also the PostgreSQL pg_buffercache extension to analyze the buffer cache. For more information, see pg_buffercache in the PostgreSQL documentation.

For more information, see Introduction to Aurora PostgreSQL cluster cache management.

Examples

The following example shows the results of calling the aurora_ccm_status function. This first example shows CCM statistics.

=> SELECT * FROM aurora_ccm_status();
 buffers_sent_last_minute | buffers_found_last_minute | buffers_sent_last_scan | buffers_found_last_scan | buffers_sent_current_scan | buffers_found_current_scan | current_scan_progress
--------------------------+---------------------------+------------------------+-------------------------+---------------------------+----------------------------+-----------------------
                  2242000 |                   2242003 |               17920442 |                17923410 |                  14098000 |                   14100964 |              15877443

For more complete detail, you can use expanded display, as shown following:

\x
Expanded display is on.
SELECT *  FROM aurora_ccm_status();
[ RECORD 1 ]-----------------------+---------
buffers_sent_last_minute           | 2242000
buffers_found_last_minute          | 2242003
buffers_sent_last_scan             | 17920442
buffers_found_last_scan            | 17923410
buffers_sent_current_scan          | 14098000
buffers_found_current_scan         | 14100964
current_scan_progress              | 15877443

This example shows how to check warm rate and warm percentage.

=> SELECT buffers_sent_last_minute * 8/60 AS warm_rate_kbps,
100 * (1.0-buffers_sent_last_scan/buffers_found_last_scan) AS warm_percent 
FROM aurora_ccm_status ();
 warm_rate_kbps | warm_percent
----------------+--------------
 16523 |        100.0