5.2 Monitoring True Cache with the V$TRUE_CACHE_STAT View

Use the V$TRUE_CACHE_STAT view to monitor True Cache statistics, including apply lag, transport lag, and block fetch latency.

Query V$TRUE_CACHE_STAT on True Cache. On the primary database this query returns no rows.

To use this view, enter the following query:

SELECT * FROM v$true_cache_stat;

The following example shows output:

MY_DGID    REMOTE_DGID    DEST_ID NAME                         VALUE        UNIT                         TIME_COMPUTED       DATA_TIME           CON_ID
---------- ----------- ---------- ---------------------------- ------------ ---------------------------- ------------------- ------------------- ------
3767970343  4224862145          0 single block fetch latency   3091         micro seconds per block      04/23/2025 21:12:10                          0
3767970343  4224862145          0 multiblock fetch latency     3432         micro seconds per request    04/23/2025 21:12:10                          0
3767970343  4224862145          0 list of blocks fetch latency 3663         micro seconds per request    04/23/2025 21:12:10                          0
3767970343  4224862145          0 prewarm progress             28.35        percentage completed         04/23/2025 21:12:10                          0
                                  transport lag                +00 00:00:00 day(2) to second(0) interval 04/23/2025 21:12:10 04/23/2025 21:12:09      0
                                  apply lag                    +00 00:00:00 day(2) to second(0) interval 04/23/2025 21:12:10 04/23/2025 21:12:09      0
                                  apply finish time                         day(2) to second(3) interval 04/23/2025 21:12:10                          0
                                  estimated startup time                    second                       04/23/2025 21:12:10                          0

5.2.1 V$TRUE_CACHE_STAT Columns

The following table describes the columns in the V$TRUE_CACHE_STAT view.

Column	Datatype	Description
MY_DGID	NUMBER	Data Guard hash ID for True Cache
REMOTE_DGID	NUMBER	Data Guard hash ID for the primary database
DEST_ID	NUMBER	Log archive destination parameter identifier The value of this column is always 0.
NAME	VARCHAR2(32)	Name of the metric: apply lag - Apply lag is a measure of the degree to which the data in True Cache lags behind the data in the primary database, due to delays in propagating and applying redo to True Cache. list of blocks fetch latency - The average latency of True Cache while fetching blocks from the primary database in list of blocks fetch mode. multiblock fetch latency - The average latency of True Cache while fetching blocks from the primary database in multiblock fetch mode. prewarm progress - The current progress of True Cache prewarming its own buffer cache by proactively fetching the list of blocks remembered from the last warmed up state, that is, from the previous instance lifetime. single block fetch latency - The average latency of True Cache while fetching blocks from the primary database in single block fetch mode. transport lag - Transport lag is a measure of the degree to which the transport of redo to True Cache lags behind the generation of redo on the primary database. If there are one or more redo gaps on True Cache, the transport lag is calculated as if no redo has been received after the beginning of the earliest redo gap. Note: The apply finish time and estimated startup time metrics are not meaningful on a True Cache and can be ignored.
VALUE	VARCHAR2(64)	Value of the metric
UNIT	VARCHAR2(32)	Unit of measurement
TIME_COMPUTED	VARCHAR2(32)	Local time on True Cache when the metric was computed
DATA_TIME	VARCHAR2(32)	Local time on True Cache when the data used to compute the metric was received The apply lag and transport lag metrics are computed based on data that is periodically received from the primary database. An unchanging value in this column across multiple queries indicates that True Cache is not receiving data from the primary database.
CON_ID	NUMBER	The ID of the container to which the data pertains. The value of this column is always 0 (CDB$ROOT container).