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
---------- ----------- ------- ---------------------------- ---------------- ---------------------------- ------------------- ------------------- ------
1797054075  3947463326       0 single block fetch latency   1612             micro seconds per block      10/01/2026 21:00:13                          0
1797054075  3947463326       0 multiblock fetch latency     1862             micro seconds per request    10/01/2026 21:00:13                          0
1797054075  3947463326       0 list of blocks fetch latency 2020             micro seconds per request    10/01/2026 21:00:13                          0
1797054075  3947463326       0 RAM buffer hit ratio         68.84            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 Flash buffer hit ratio       18.22            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 True Cache hit ratio         74.52            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 Ram buffer usage ratio       75.04            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 Flash buffer usage ratio     99.96            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 True cache usage ratio       86.27            percentage ratio             10/01/2026 21:00:13                          0
1797054075  3947463326       0 prewarm progress             100.00           percentage completed         10/01/2026 21:00:13                          0
                               transport lag                +00 00:00:00     day(2) to second(0) interval 10/01/2026 21:00:13 10/01/2026 21:00:12      0
                               apply lag                    +00 00:00:00     day(2) to second(0) interval 10/01/2026 21:00:13 10/01/2026 21:00:12      0
                               apply finish time            +00 00:00:00.000 day(2) to second(3) interval 10/01/2026 21:00:13                          0
                               estimated startup time                        second                       10/01/2026 21:00:13                          0

14 rows selected.

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. RAM buffer hit ratio - Percentage of data requests served from the RAM buffer cache. Flash buffer hit ratio - Percentage of data requests served from the DB flash cache. True Cache hit ratio - Percentage of data requests served from True Cache without fetching data from the primary database. RAM buffer usage ratio - Number of RAM buffer cache buffers in use as a percent of the total number of RAM buffer cache buffers. Flash buffer usage ratio - Number of DB flash cache buffers in use as a percent of the total number of DB flash cache buffers. True Cache usage ratio - Combines RAM buffer usage ratio and flash buffer usage ratio to generate a total of True Cache buffers in use as a percent of total available buffers. 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).

Related Topics

V$TRUE_CACHE_STAT