Qlik Replicate: Redo Thread vs OCI thread for Oracle Source

[shashi_holla]

This article highlights the difference between redo log thread vs the OCI thread used by ASM for Oracle source endpoints.

REDO Thread (defined in Oracle RAC instances)

[SOURCE_CAPTURE  ]I:  Start processing archived Redo log sequence 174669 thread 1 name +RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174669.8435.1172797103  (oradcdc_redo.c:1011)
[SOURCE_CAPTURE  ]I:  Start processing archived Redo log sequence 154324 thread 2 name +RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_2_seq_154324.11355.1172797615  (oradcdc_redo.c:1011)

The two threads which you are seeing above are the two redo threads defined for a 2 node Oracle RAC database.

A redo thread is a set of redo log files that an Oracle instance uses to log changes made to the database. Each instance in an RAC environment has its own redo thread.

That is why you will see 2 different sequences for both the threads:

log sequence 174669 thread 1
log sequence 154324 thread 2

OCI Thread (Number of concurrent ASM Read threads which we define at replicate end)

[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '0'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '1'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '2'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '3'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '4'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '5'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '6'  (oradcdc_io.c:864)
[SOURCE_CAPTURE  ]T:  ASM file '+RECO/P50K266N/ARCHIVELOG/2024_06_28/thread_1_seq_174694.1245.1172802097' opened. Params: block size '512', block count '7389811', redo thread id '1' OCI Thread Id: '7'  (oradcdc_io.c:864)

The above 8 OCI Thread Ids in the logs are the 8 ASM parallel read threads which the Qlik Replicate task has opened to read a single archived redo log file.

Environment

• Qlik Replicate