This section contains information about:
- The behavior of how Datastream handles data that's being pulled from a source Oracle database
- The versions of Oracle database that Datastream supports
- An overview of how to setup a source Oracle database so that data can be streamed from it to a destination
- Known limitations for using Oracle database as a source
Behavior
The source Oracle database relies upon its Oracle Logminer feature for exposing changes to the data.
- All schemas or specific schemas from a given database, as well as all tables from the schemas or specific tables, can be selected.
- All historical data is replicated.
- All data manipulation language (DML) changes, such as inserts, updates, and deletes from the specified databases and tables, are replicated.
- Datastream replicates both committed and, in some cases, uncommitted changes into the destination. Datastream reads uncommitted changes. In case of a rollback, the Datastream output records also include the opposite operation. For example, if there's a rolled-back
INSERT
operation, then the output records will also contain a correspondingDELETE
operation. In this case, the event will appear as aDELETE
event with only theROWID
.
ROWID
based backfill
In Oracle, ROWID
is a pseudocolumn that stores unique identifiers for rows in a table. Datastream uses the ROWID
values for its backfill operations. Because of this, we recommend that you don't perform any actions that could change the ROWID
values in your source Oracle database until the backfill operation completes.
The actions that can change the ROWID
values include:
Physical movement of rows:
- Export and import operations: when you export a table, and then you import it back, the physical location of rows might change, resulting in new
ROWID
values. ALTER TABLE (...) MOVE
command: moving a table to a different tablespace can change the physical storage and lead toROWID
changes.ALTER TABLE (...) SHRINK SPACE
command: this command compresses the table, potentially moving rows and affecting theirROWID
values.- Partitioning operations: splitting, merging, or moving partitions can change the physical placement of rows and their
ROWID
values.
- Export and import operations: when you export a table, and then you import it back, the physical location of rows might change, resulting in new
Flashback operations:
FLASHBACK TABLE
command: restoring a table to a previous state involves deleting and re-inserting rows, thus creating newROWID
values.FLASHBACK_TRANSACTION_QUERY
: Similar toFLASHBACK TABLE
. Rolling back a transaction can causeROWID
changes if rows were deleted or updated within the transaction.
Versions
Datastream supports the following versions of Oracle database:
- Oracle 11g, Version 11.2.0.4
- Oracle 12c, Version 12.1.0.2
- Oracle 12c, Version 12.2.0.1
- Oracle 18c
- Oracle 19c
- Oracle 21c
Datastream supports the following types of Oracle database:
- Self-hosted on-premises or on any cloud provider
- Amazon RDS for Oracle
- Oracle Cloud
- Oracle Exadata
- Oracle RAC
- Oracle Active Data Guard standby database
Setup
To set up a source Oracle database so that data from it can be streamed into a destination, you must configure the database to grant access, set up logging, define a retention policy, and so on.
See Configure a source Oracle database to learn how to configure this database so that Datastream can pull data from it into a destination.
Known limitations
Known limitations for using Oracle database as a source include:
- Streams are limited to 10,000 tables. If a stream includes more than 10,000 tables, then it might run into errors.
- Datastream supports Oracle multi-tenant architecture (CDB/PDB), however, you can only replicate a single pluggable database in a stream.
- Oracle Autonomous Database isn't supported.
- For tables that don't have a primary key, Datastream uses the row's
ROWID
to perform a merge operation on the consumer side. Note that theROWID
might not be unique. If you delete and reinsert a row with Oracle's Export/Import utility, for example, then the row'sROWID
might change. If you delete a row, then Oracle can reassign itsROWID
to a new row inserted later. - Index-organized tables (IOTs) aren't supported.
- Temporary tables aren't supported.
- Columns of data types
ANYDATA
,BFILE
,INTERVAL DAY TO SECOND
,INTERVAL YEAR TO MONTH
,LONG/LONG RAW
,SDO_GEOMETRY
,UDT
,UROWID
,XMLTYPE
aren't supported, and are replaced withNULL
values. - To stream columns of large object data types, such as binary large objects (
BLOB
), character large objects (CLOB
) and national character large objects (NCLOB
), you need to include thestreamLargeObjects
flag in your stream configuration. If you don't include the flag, Datastream doesn't stream such columns and they're replaced withNULL
values in the destination. For more information, see Enable streaming of large objects for Oracle sources. - For Oracle 11g, tables that have columns of data types
ANYDATA
orUDT
aren't supported, and the entire table won't be replicated. - Oracle Label Security (OLS) isn't replicated.
- Datastream periodically fetches the latest schema from the source as events are processed. If a schema changes, then some events from the new schema might be read while the old schema is still applied. In this case, Datastream detects the schema change, triggers a schema fetch, and reprocesses the failed events.
- Not all changes to the source schema can be detected automatically, in which case data corruption may occur. The following schema changes may cause data corruption or failure to process the events downstream:
- Dropping columns
- Adding columns to the middle of a table
- Changing the data type of a column
- Reordering columns
- Dropping tables (relevant if the same table is then recreated with new data added)
- Truncating tables
- Datastream doesn't support replicating views.
- Datastream supports materialized views. However, new views created while the stream is running aren't backfilled automatically.
SAVEPOINT
statements aren't supported and can cause data discrepancy in case of a rollback.- Datastream supports the following character set encodings for Oracle databases:
AL16UTF16
AL32UTF8
IN8ISCII
JA16SJIS
JA16SJISTILDE
US7ASCII
UTF8
WE8ISO8859P1
WE8ISO8859P9
WE8ISO8859P15
WE8MSWIN1252
ZHT16BIG5
- Datastream doesn't support replicating zero date values. Such dates are replaced with
NULL
values. - Generating very large log files might cause Datastream to time out, which can lead to stream failure. The recommended redo log file size is under 1GB.
- Datastream doesn't support direct connectivity to databases using the Single Client Access Name (SCAN) feature in Oracle Real Application Clusters (RAC) environments. For information about potential solutions, see Oracle source behavior and limitations.
- If the source is an Oracle Active Data Guard standby database, Datastream doesn't support replicating encrypted data.
What's next
- Learn how to configure an Oracle source for use with Datastream.