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http://blog.itpub.net/28258625/viewspace-2060713
This knowledge document describes a best practice method for handling tables without primary keys or unique indexes when using Oracle GoldenGate to replicate transactional data between Oracle databases.
There is a change log at the end of this document.
This document is divided into the following sections:
Appendix A: Sample Table Configuration
In order to maintain data integrity when replicating transactional data, Oracle GoldenGate will use primary key columns or unique index columns to uniquely identify a row when issuing update or delete statements against the target database. If no primary keys or unique indexes exist on the table being replicated, Oracle GoldenGate will use all columns to uniquely identify a row.
It is perfectly acceptable to use all columns to uniquely identify a row under the following conditions:
If the table being replicated does not meet all of the conditions listed above, it is recommended to add a column to the table with a SYS_GUID default value to uniquely identify the row. The next section describes the detailed steps on how to configure a table without a primary key or unique index in order to uniquely identify each row.
| Software Component | Minimum Version |
|---|---|
| Oracle Database |
10.2 or greater |
| Oracle GoldenGate | 10.4 or greater |
2.1 Configure Table(s) in Source Database
Before instantiating the target database from a copy of source, perform. the following steps to the table(s) without primary keys or unique indexes.
Step 1 - Add Column to Table
Issue the following command to add the column to the table.
Replace <table_name> with the table name being modified.
Step 2 - Modify Column Data Default to Use SYS_GUID Values
Issue the following command to modify the OGG_KEY_ID default value to use SYS_GUID values. SYS_GUID values are unique values generated from an internal Oracle algorithm.
Immediately after modifying the OGG_KEY_ID column, newly inserted rows will automatically populate the OGG_KEY_ID column with SYS_GUID values.
Replace <table_name> with the table name being modified.
Note : DO NOT combine steps 1 and 2 into 1 SQL statement. Doing so will cause Oracle to populate the OGG_KEY_ID column with a full table lock. The table could be locked for a significant amount of time based on the number of existing rows in the table.
Step 3 - Backfill Existing Table Rows with SYS_GUID Values
Now that newly inserted rows are being handled, the OGG_KEY_ID column still needs to be populated for existing table rows. The following SQL script. will backfill the existing table rows with unique SYS_GUID values.
Replace <table_name> with the table name being updated.
DECLARE cursor C1 is select ROWID from
<table_name>
where OGG_KEY_ID is null;
finished number:=0; commit_cnt number:=0; err_msg varchar2(150);
snapshot_too_old exception; pragma exception_init(snapshot_too_old, -1555);
old_size number:=0; current_size number:=0;
BEGIN
while (finished=0) loop
finished:=1;
BEGIN
for C1REC in C1 LOOP
update
<table_name>
set GG_PK_ID = sys_guid()
where ROWID = C1REC.ROWID;
commit_cnt:= commit_cnt + 1;
IF (commit_cnt = 10000) then
commit;
commit_cnt:=0;
END IF;
END LOOP;
EXCEPTION
when snapshot_too_old then
finished:=0;
when others then
rollback;
err_msg:=substr(sqlerrm,1,150);
raise_application_error(-20555, err_msg);
END;
END LOOP;
IF(commit_cnt > 0) then
commit;
END IF;
END;
/
Note : This process could take a significant amount of time to complete based on the number of existing rows in the table. The script. will not perform. a full table lock and will only lock each row exclusively as it updates it.
Step 4 - Create Table Supplemental Log Group in Source Database
Issue the following commands in GGSCI to create the table supplemental log group using the OGG_KEY_ID column. This forces Oracle to always write the OGG_KEY_ID value to the online redo logs.
Replace <username> with source database username.
Replace <password> with source database user's password.
Replace <owner> with table schema owner.
Replace <table_name> with the table name being modified.
GGSCI> dblogin userid <username> , password <password>
GGSCI> add trandata <owner> . <table_name> , COLS (OGG_KEY_ID), nokey
Step 1 - Create Unique Index on Target Table
After instantiating the target database, issue the following command to add a unique index to the table. The unique index prevents full table scans when applying update and delete statements to the target database.
Replace <table_name> with the table name the unique index is on.
Replace <tablespace_name> with tablespace name to store unique index.
create unique index OGG_ <table_name> _UI on <table_name> (OGG_KEY_ID) logging online tablespace <tablespace_name>
Note : This process could take a significant amount of time to complete based on the number of existing rows in the table.
Step 1 - Specify OGG_KEY_ID for Table Key in Extract Parameter File
Use the KEYCOLS parameter in the Extract parameter file to define OGG_KEY_ID as the unique column for the table.
Replace <table_name> with the table name the unique index is on.
TABLE <table_name> , KEYCOLS (OGG_KEY_ID);
For further information about using Oracle GoldeGate, refer to the following documents available on edelivery:
Add Column to Table
SQL> SELECT * FROM NL_WEST;
TEAM_NAME LOCATION
---------------- --------------------
PADRES SAN DIEGO
ROCKIES COLORADO
DODGERS LOS ANGELES
DIAMONDBACKS ARIZONA
SQL> alter table NL_WEST add OGG_KEY_ID raw(16);
Table altered.
SQL> select * from NL_WEST;
TEAM_NAME LOCATION OGG_KEY_ID
---------------- ------------------ ----------------
PADRES SAN DIEGO
ROCKIES COLORADO
DODGERS LOS ANGELES
DIAMONDBACKS ARIZONA
Modify Column Data Default to Use SYS_GUID() Values
SQL> alter table NL_WEST modify OGG_KEY_ID default sys_guid();
Table altered.
SQL> select * from NL_WEST;
TEAM_NAME LOCATION OGG_KEY_ID
--------------- ------------------ ----------------
PADRES SAN DIEGO
ROCKIES COLORADO
DODGERS LOS ANGELES
DIAMONDBACKS ARIZONA
SQL> INSERT INTO NL_WEST (TEAM_NAME,LOCATION) VALUES ('GIANTS','SAN FRANCISCO');
1 row created.
SQL> COMMIT;
Commit complete.
SQL> select * from NL_WEST;
TEAM_NAME LOCATION OGG_KEY_ID
---------------- ---------------- ----------------
PADRES SAN DIEGO
ROCKIES COLORADO
DODGERS LOS ANGELES
DIAMONDBACKS ARIZONA
GIANTS SAN FRANCISCO 95AB2831E724991FE040C8C86E0162D0
Backfill Existing Table Rows with SYS_GUID() Values
SQL> DECLARE cursor C1 is select ROWID from
NL_WEST
where OGG_KEY_ID is null;
2 3 4 finished number:=0; commit_cnt number:=0; err_msg varchar2(150);
5 snapshot_too_old exception; pragma exception_init(snapshot_too_old, -1555);
6 old_size number:=0; current_size number:=0;
7 BEGIN
8 while (finished=0) loop
9 finished:=1;
10 BEGIN
11 for C1REC in C1 LOOP
12 update NL_WEST
13 set OGG_KEY_ID = sys_guid()
14 where ROWID = C1REC.ROWID;
15 commit_cnt:= commit_cnt + 1;
16 IF (commit_cnt = 10000) then
17 commit;
18 commit_cnt:=0;
19 END IF;
20 END LOOP;
21 EXCEPTION
22 when snapshot_too_old then
23 finished:=0;
24 when others then
25 rollback;
26 err_msg:=substr(sqlerrm,1,150);
27 raise_application_error(-20555, err_msg);
28 END;
END LOOP;
29 30 IF(commit_cnt > 0) then
31 commit;
32 END IF;
33 END;
34 /
PL/SQL procedure successfully completed.
SQL> select * from NL_WEST;
TEAM_NAME LOCATION OGG_KEY_ID
---------------- ---------------- ----------------
PADRES SAN DIEGO 95AB2831E725991FE040C8C86E0162D0
ROCKIES COLORADO 95AB2831E726991FE040C8C86E0162D0
DODGERS LOS ANGELES 95AB2831E727991FE040C8C86E0162D0
DIAMONDBACKS ARIZONA 95AB2831E728991FE040C8C86E0162D0
GIANTS SAN FRANCISCO 95AB2831E724991FE040C8C86E0162D0
Create Table Supplemental Log Group in Source Database
GGSCI> dblogin userid OGG, password OGG
GGSCI> add trandata MLB.NL_WEST, COLS (OGG_KEY_ID), nokey
Create Unique Index on Target Table
SQL> create unique index GG_NL_WEST_UI on NL_WEST (OGG_KEY_ID) logging online;
Index created.
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