# Troubleshooting Oracle GoldenGate
This section explains the most common issues when using Oracle GoldenGate with Amazon RDS for Oracle.
**Topics**
+ [Error opening an online redo log](#Appendix.OracleGoldenGate.Troubleshooting.Logs)
+ [Oracle GoldenGate appears to be properly configured but replication is not working](#Appendix.OracleGoldenGate.Troubleshooting.Replication)
+ [Integrated REPLICAT slow due to query on SYS."\$1DBA\$1APPLY\$1CDR\$1INFO"](#Appendix.OracleGoldenGate.IR)
## Error opening an online redo log
Make sure that you configure your databases to retain archived redo logs. Consider the following guidelines:
+ Specify the duration for log retention in hours. The minimum value is one hour.
+ Set the duration to exceed any potential downtime of the source DB instance, any potential period of communication, and any potential period of networking issues for the source DB instance. Such a duration lets Oracle GoldenGate recover logs from the source DB instance as needed.
+ Ensure that you have sufficient storage on your instance for the files.
If you don't have log retention enabled, or if the retention value is too small, you receive an error message similar to the following.
```
2022-03-06 06:17:27 ERROR OGG-00446 error 2 (No such file or directory)
opening redo log /rdsdbdata/db/GGTEST3_A/onlinelog/o1_mf_2_9k4bp1n6_.log for sequence 1306
Not able to establish initial position for begin time 2022-03-06 06:16:55.
```
## Oracle GoldenGate appears to be properly configured but replication is not working
For pre-existing tables, you must specify the SCN that Oracle GoldenGate works from.
**To fix this issue**
1. Log in to the source database and launch the Oracle GoldenGate command line interface (`ggsci`). The following example shows the format for logging in.
```
dblogin userid oggadm1@OGGSOURCE
```
1. Using the `ggsci` command line, set up the start SCN for the `EXTRACT` process. The following example sets the SCN to 223274 for the `EXTRACT`.
```
ALTER EXTRACT EABC SCN 223274
start EABC
```
1. Log in to the target database. The following example shows the format for logging in.
```
dblogin userid oggadm1@OGGTARGET
```
1. Using the `ggsci` command line, set up the start SCN for the `REPLICAT` process. The following example sets the SCN to 223274 for the `REPLICAT`.
```
start RABC atcsn 223274
```
## Integrated REPLICAT slow due to query on SYS."\$1DBA\$1APPLY\$1CDR\$1INFO"
Oracle GoldenGate Conflict Detection and Resolution (CDR) provides basic conflict resolution routines. For example, CDR can resolve a unique conflict for an `INSERT` statement.
When CDR resolves a collision, it can insert records into the exception table `_DBA_APPLY_CDR_INFO` temporarily. Integrated `REPLICAT` deletes these records later. In a rare scenario, the integrated `REPLICAT` can process a large number of collisions, but a new integrated `REPLICAT` does not replace it. Instead of being removed, the existing rows in `_DBA_APPLY_CDR_INFO` are orphaned. Any new integrated `REPLICAT` processes slow down because they are querying orphaned rows in `_DBA_APPLY_CDR_INFO`.
To remove all rows from `_DBA_APPLY_CDR_INFO`, use the Amazon RDS procedure `rdsadmin.rdsadmin_util.truncate_apply$_cdr_info`. This procedure is released as part of the October 2020 release and patch update. The procedure is available in the following database versions:
+ [ Version 21.0.0.0.ru-2022-01.rur-2022-01.r1](https://docs.aws.amazon.com/AmazonRDS/latest/OracleReleaseNotes/oracle-version-21-0.html#oracle-version-RU-RUR.21.0.0.0.ru-2022-01.rur-2022-01.r1) and higher
+ [ Version 19.0.0.0.ru-2020-10.rur-2020-10.r1](https://docs.aws.amazon.com/AmazonRDS/latest/OracleReleaseNotes/oracle-version-19-0.html#oracle-version-RU-RUR.19.0.0.0.ru-2020-10.rur-2020-10.r1) and higher
The following example truncates the table `_DBA_APPLY_CDR_INFO`.
```
SET SERVEROUTPUT ON SIZE 2000
EXEC rdsadmin.rdsadmin_util.truncate_apply$_cdr_info;
```