Verifying Redo Transport Compression in 11.2, 12.1 and 12.2 Data Guard Configuraitons

Redo shipped to standby could be compressed for transport in two ways. One is external to the database and uses SSH tunnelling. Other method is enabling compression for the remote log archive destination. Second option requires advance compression license. Once redo transport compression (RTC) is enabled it could verified by enabling log archive tracing. However, there's a difference as to level of tracing and information for DB versions 11.2, 12.1 and 12.2. This posts explore these variations.

Verifying RTC in 11.2.0.4
The DG configuration for 11.2 is as follows

DGMGRL> show configuration

Configuration - db_dg

  Protection Mode: MaxAvailability
  Databases:
    prod  - Primary database
    stdby - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

Enable RTC on the standby database. This updates the log archive destination setting on the primary by adding compression=enable option.

DGMGRL> edit database stdby set property RedoCompression='enable';
Property "redocompression" updated

On the alert log of the primary following could be seen.

Tue Aug 14 14:29:41 2018
ALTER SYSTEM SET log_archive_dest_3='service="stdbytns"','LGWR SYNC AFFIRM delay=0 optional compression=enable max_failure=10 max_connections=5 reopen=180 db_unique_name="stdby" net_timeout=30','valid_for=(all_logfiles,primary_role)' SCOPE=BOTH;

Enabling log archive tracing level of 1 for primary database

DGMGRL>  edit database prod set property LogArchiveTrace='1';
Property "logarchivetrace" updated

Enable log archive tracing level of 16 for standby

DGMGRL> edit database stdby set property LogArchiveTrace='16';
Property "logarchivetrace" updated

With these setting in place on the primary *nss*.trc files will contain entries similar to following to show that RTC is enabled.

RTC: Compression ratio for this I/O is 81%
RTC: Compression ratio for this I/O is 81%
RTC: Compression ratio for this I/O is 81%
RTC: Compression ratio for this I/O is 80%

On the standby the decompression information is shown in *rsf*.trc files as follows

RTC: decompressed 94 bytes to 512 bytes
RTC: decompressed 93 bytes to 512 bytes
RTC: decompressed 99 bytes to 512 bytes
RTC: decompressed 88 bytes to 512 bytes
RTC: decompressed 5221 bytes to 24576 bytes

If the tracing on the primary is increased to 16 (which Oracle document says as "Track detailed ARCHIVELOG destination activity") only limited RTC information is given out.

edit database prod set property LogArchiveTrace='16';

Both *arc*.trc and *lgwr*.trc files will have entries similar to following.

cat prod_arc7_3372.trc | grep RTC
RTC enabled.
cat prod_lgwr_3297.trc | grep RTC
RTC enabled.
RTC enabled.

Verifying RTC in 12.1.0.2
The 12.1.0.2 DG configuration is as follows

DGMGRL> show configuration;

Configuration - ent12c1_dgb

  Protection Mode: MaxAvailability
  Members:
  ent12c1  - Primary database
    fs12c1   - Far sync instance
      ent12c1s - Physical standby database

  Members Not Receiving Redo:
  fs12c1s  - Far sync instance

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS

On 12.1 setting log archive trace to 1 has no effect on tracing RTC. Setting the value to 16 on primary gives descriptive RTC information which indicates if RTC is enabled or not.

DGMGRL>  edit database ent12c1 set property logarchivetrace='16';
Property "logarchivetrace" updated

The RTC related information appear in *arc*.trc files and *tt*.trc files

cat ent12c1_arc3_15498.trc | grep RTC
RTC enabled.
RTC: Allocating 11534336 buffer bytes for compression.
RTC: header-batch write block 1, count 1 - RTC disabled
RTC: Enable compression for subsequent batches
RTC: actual compressed bytes# 1295

cat ent12c1_tt01_15532.trc | grep RTC
RTC enabled.
Re-enabling RTC following backoff interval 1.
RTC: actual compressed bytes# 10270
RTC: actual compressed bytes# 536
RTC: actual compressed bytes# 1697
RTC: actual compressed bytes# 508

Redo compression could be enabled on far sync instances as well. Setting trace level to 16 on far sync instance will also generate RTC information on far sync trace files.

DGMGRL> edit far_sync fs12c1 set property RedoCompression='enable';
Property "redocompression" updated

DGMGRL> edit far_sync fs12c1 set property LogArchiveTrace='16';
Property "logarchivetrace" updated

cat fs12c1_tt00_2515.trc | grep RTC
RTC: actual compressed bytes# 97
RTC: actual compressed bytes# 79

To get decompression related information from standby set log archive trace value to 1024 (1024: Tracks RFS physical client).

DGMGRL> edit database ent12c1s set property logarchivetrace='1024';
Property "logarchivetrace" updated

Decompression related information is shown in *rfs*.trc files.

cat ent12c1s_rfs_8859.trc | grep RTC
RTC: decompressed 79 bytes to 512 bytes
RTC: decompressed 81 bytes to 512 bytes
RTC: decompressed 97 bytes to 512 bytes
RTC: decompressed 79 bytes to 512 bytes

Verifying RTC in 12.2.0.1 (and 18.3.0.0)
The 12.2 DG configuration is as follows

DGMGRL> show configuration

Configuration - dg12c2

  Protection Mode: MaxAvailability
  Members:
  prodcdb - Primary database
    stbycdb - Physical standby database

Fast-Start Failover: DISABLED

Configuration Status:
SUCCESS   (status updated 35 seconds ago)

On 12.2 setting log archive trace to 16 on primary generates the RTC information.

DGMGRL> edit database prodcdb set property LogArchiveTrace='16';
Property "logarchivetrace" updated

The RTC information is available on *lgwr*.trc and *nss*.trc files.

cat prodcdb_lgwr_2616.trc | grep RTC
RTC enabled.
RTC enabled.
RTC enabled.

cat prodcdb_nss2_2708.trc | grep RTC
RTC: Enable compression following header-only I/O
RTC: Enable compression following header-only I/O
RTC: Enable compression following header-only I/O

No other values such as 512 (512: Tracks LGWR redo shipping network activity) or combination of values seems to give more descriptive information such as compression ratio or compressed bytes as in the case with previous versions. However, decompression information on standby could be traced with 1024.

DGMGRL> edit database stbycdb set property LogArchiveTrace='1024';
Property "logarchivetrace" updated

Decompression information available in *rfs*.trc file.

cat stbycdb_rfs_2243.trc
krsr_rfs_wda: RTC: decompressed 82 bytes to 512 bytes
krsr_rfs_wda: RTC: decompressed 81 bytes to 512 bytes
krsr_rfs_wda: RTC: decompressed 675 bytes to 1536 bytes
krsr_rfs_wda: RTC: decompressed 1167 bytes to 3072 bytes
krsr_rfs_wda: RTC: decompressed 76 bytes to 512 bytes

Useful Metalink Notes
How to confirm if Redo Transport Compression is used In Oracle Data Guard? [ID 1927057.1]
Redo Transport Compression in a Data Guard Environment [ID 729551.1]
LOG_ARCHIVE_TRACE=16 DOES NOT SHOW REDO COMPRESSION DETAIL IN LOG TRANSPORT in 11gr2 [ID 2193605.1]
How to find out the compression rate of Redo Transport Compression ? [ID 1490751.1]