Checkpoint Tables Additional Details

When database checkpoints are being used, Oracle GoldenGate creates a checkpoint table with a user-defined name in the database upon execution of the ADD CHECKPOINTTABLE command, or a user can create the table by using the chkpt_db_create.sql script (where db is an abbreviation of the type of database that the script supports).

There are two tables: the main checkpoint table and an auxiliary checkpoint table that is created automatically. The auxiliary table, known as the transaction table, bears the name of the primary checkpoint table appended with _lox. Each Replicat, or each thread of a coordinated Replicat, uses one row in the checkpoint table to store its progress information.

At checkpoint time, there typically are some number of transactions (among the total n transactions) that were applied, and the rest are still in process. For example, if Replicat is processing a group of n transactions ranging from CSN1 to CSN3. CSN1 is the high watermark and CSN3 is the low watermark. Any transaction with a CSN higher than the high watermark has not been processed, and any transaction with a CSN lower than the low watermark has already been processed. Completed transactions are stored in the LOG_CMPLT_XID column of the checkpoint table. Any overflow of these transactions is stored in the transaction table (auxiliary checkpoint table) in the LOG_CMPLT_XID column of that table.

Currently, Replicat (or each Replicat thread of a coordinated Replicat) applies transactions serially (not in parallel); therefore, the high watermark (the LOG_CSN value in the table) is always the same as the low watermark (the LOG_CMPLT_CSN value in the table), and there typically is only one transaction ID in the LOG_CMPLT_XID column. The only exception is when there are multiple transactions sharing the same CSN.

Do not change the names or attributes of the columns in these tables. You can change table storage attributes as needed.

Column	Description
`LOG_BSN`	The `LOG_BSN` provides information needed to set Extract back in time to reprocess transactions. Some filtering by Replicat is necessary because Extract will likely re-generate a small amount of data that was already applied by Replicat.
`VERSION`	The version of the checkpoint table format. Enables future enhancements to be identified as version numbers of the table.
`AUDIT_TS`	The timestamp of the commit of the source transaction.
`SEQNO`	The sequence number of the input trail that Replicat was reading at the time of the checkpoint.
`RBA`	The relative byte address that Replicat reached in the trail identified by `SEQNO`. `RBA` + `SEQNO` provide an absolute position in the trail that identifies the progress of Replicat at the time of checkpoint.
`GROUP_NAME (primary key)`	The name of a Replicat group using this table for checkpoints. There can be multiple Replicat groups using the same table. This column is part of the primary key.
`LAST_UPDATE_TS`	The date and time when the checkpoint table was last updated.
`CREATE_TS`	The date and time when the checkpoint table was created.
`CURRENT_DIR`	The current Oracle GoldenGate home directory or folder.
`LOG_CMPLT_XIDS`	Stores the transactions between the high and low watermarks that are already applied.
`LOG_CMPLT_CSN`	Stores the low watermark, or the lower boundary, of the CSNs. Any transaction with a lower CSN than this value has already been processed.
`LOG_CSN`	Stores the high watermark, or the upper boundary, of the CSNs. Any transaction with a CSN higher than this value has not been processed.
`LOG_XID`	Not used. Retained for backward compatibility.
`GROUP_KEY (primary key)`	A unique identifier that, together with `GROUPNAME` , uniquely identifies a checkpoint regardless of how many Replicat groups are writing to the same table. This column is part of the primary key.

Column	Description
`GROUP_KEY`	A unique identifier that, together with `GROUPNAME`, uniquely identifies a checkpoint regardless of how many Replicat groups are writing to the same table. This column is part of the primary key of the transaction table.
`LOG_CMPLT_XIDS_SEQ`	Creates unique rows in the event there are so many overflow transactions that multiple rows are required to store them all. This column is part of the primary key of the transaction table.
`LOG_CMPLT_XIDS`	Stores the overflow of transactions between the high and low watermarks that are already applied.
`LOG_CMPLT_CSN`	The foreign key that references the checkpoint table. This column is part of the primary key of the transaction table.
`GROUP_NAME`	The name of a Replicat group using this table for checkpoints. There can be multiple Replicat groups using the same table. This column is part of the primary key of the transaction table.

Internal Checkpoint Information

The INFO command with the SHOWCH option not only displays current checkpoint entries, but it also displays metadata information about the record itself. This information is not documented and is for use by the Oracle GoldenGate processes and by support personnel when resolving a support case.

The metadata is contained in the following entries in the SHOWCH output.

Header:

    Version = 2

    Record Source = A

    Type = 1

    # Input Checkpoints = 1

    # Output Checkpoints = 0

    File Information:

    Block Size = 2048

    Max Blocks = 100

    Record Length = 2048

    Current Offset = 0

    Configuration:

    Data Source = 0

    Transaction Integrity = -1

    Task Type = 0

    Status:
    
    Start Time = 2011-01-12 13:10:13

    Last Update Time = 2011-01-12 21:23:31

    Stop Status = A

    Last Result = 400

INFO EXTRACT SHOWCH Command: Checkpoint Information

The following sample presents the checkpoint information returned by the INFO EXTRACT command with the SHOWCH option. In this case, the data source is an Oracle RAC database cluster, so there is thread information included in the output. You can view past checkpoints by specifying the number of them that you want to view after the SHOWCH argument.

EXTRACT JC108XT Last Started 2011-01-01 14:15 Status ABENDED
Checkpoint Lag 00:00:00 (updated 00:00:01 ago)
Log Read Checkpoint File /orarac/oradata/racq/redo01.log
 2011-01-01 14:16:45 Thread 1, Seqno 47, RBA 68748800
Log Read Checkpoint File /orarac/oradata/racq/redo04.log
 2011-01-01 14:16:19 Thread 2, Seqno 24, RBA 65657408
Current Checkpoint Detail:
Read Checkpoint #1
 Oracle RAC Redo Log
 Startup Checkpoint (starting position in data source):
 Thread #: 1
 Sequence #: 47
 RBA: 68548112
 Timestamp: 2011-01-01 13:37:51.000000
 SCN: 0.8439720
 Redo File: /orarac/oradata/racq/redo01.log

Recovery Checkpoint (position of oldest unprocessed transaction in data source):
 Thread #: 1
 Sequence #: 47
 RBA: 68748304
 Timestamp: 2011-01-01 14:16:45.000000
 SCN: 0.8440969
Redo File: /orarac/oradata/racq/redo01.log
 Current Checkpoint (position of last record read in the data source):
 Thread #: 1
 Sequence #: 47
 RBA: 68748800
 Timestamp: 2011-01-01 14:16:45.000000
 SCN: 0.8440969
 Redo File: /orarac/oradata/racq/redo01.log
Read Checkpoint #2
 Oracle RAC Redo Log
 Startup Checkpoint(starting position in data source):
 Sequence #: 24
 RBA: 60607504
 Timestamp: 2011-01-01 13:37:50.000000
 SCN: 0.8439719
 Redo File: /orarac/oradata/racq/redo04.log
Recovery Checkpoint (position of oldest unprocessed transaction in data source):
 Thread #: 2
 Sequence #: 24
 RBA: 65657408
 Timestamp: 2011-01-01 14:16:19.000000
 SCN: 0.8440613
 Redo File: /orarac/oradata/racq/redo04.log
 Current Checkpoint (position of last record read in the data source):
 Thread #: 2
 Sequence #: 24
 RBA: 65657408
 Timestamp: 2011-01-01 14:16:19.000000
 SCN: 0.8440613
 Redo File: /orarac/oradata/racq/redo04.log
Write Checkpoint #1
 GGS Log Trail
 Current Checkpoint (current write position):
 Sequence #: 2
 RBA: 2142224
 Timestamp: 2011-01-01 14:16:50.567638
 Extract Trail: ./dirdat/eh
 Header:
 Version = 2
 Record Source = A
 Type = 6
 # Input Checkpoints = 2
 # Output Checkpoints = 1
 File Information:
 Block Size = 2048
 Max Blocks = 100
 Record Length = 2048
 Current Offset = 0
Configuration:
 Data Source = 3
 Transaction Integrity = 1
 Task Type = 0
 Status:
 Start Time = 2011-01-01 14:15:14
 Last Update Time = 2011-01-01 14:16:50
 Stop Status = A
 Last Result = 400

INFO REPLICAT, SHOWCH: Checkpoint Information

The basic command shows current checkpoints. To view a specific number of previous checkpoints, type the value after the SHOWCH argument.

REPLICAT JC108RP Last Started 2011-01-12 13:10 Status RUNNING
Checkpoint Lag 00:00:00 (updated 111:46:54 ago)
Log Read Checkpoint File ./dirdat/eh000000000
 First Record RBA 3702915
Current Checkpoint Detail:
 Read Checkpoint #1
 GGS Log Trail
 Startup Checkpoint(starting position in data source):
 Sequence #: 0
 RBA: 3702915
 Timestamp: Not Available
 Extract Trail: ./dirdat/eh
 Current Checkpoint (position of last record read in the data source):
 Sequence #: 0
 RBA: 3702915
 Timestamp: Not Available
 Extract Trail: ./dirdat/eh
 Header:
 Version = 2
 Record Source = A
 Type = 1
 # Input Checkpoints = 1
 # Output Checkpoints =
 File Information:
 Block Size = 2048
 Max Blocks = 100
 Record Length = 2048
 Current Offset = 0
 Configuration:
 Data Source = 0
 Transaction Integrity = -1
 Task Type = 0
 Status:
 Start Time = 2011-01-12 13:10:13
 Last Update Time = 2011-01-12 21:23:31
 Stop Status = A
 Last Result = 400