Purge FND_LOG_MESSAGES in Oracle Application Release 11i and R12

For Purging data in "FND_LOG_MESSAGES" table, below concurrent program has to run successfully.

In Oracle Application Release 11i :
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Please run concurrent program "Purge Debug Log and System Alerts" (short name: FNDLGPRG).

In Oracle Application Release 12 :
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Please run concurrent program "Purge Logs and Closed System Alerts" (short name: FNDLGPRG).

Concurrent program "Purge Debug Log and System Alerts" in Release 11i and "Purge Logs and Closed System Alerts" in Release 12 is recommended way to purge messages. This program purges all messages up to the specified date,except messages for active transactions (new or open alerts, active ICX sessions, concurrent requests, and so on). This program is by default scheduled to run daily and purge messages whose transaction context is older than 7 days. Internally this concurrent program invokes FND_LOG_ADMIN APIs.

Data from the following tables will be deleted when you run "Purge Logs and Closed System Alerts'" or "Purge Debug Log and System Alerts" program :

FND_EXCEPTION_NOTES;
FND_OAM_BIZEX_SENT_NOTIF;
FND_LOG_METRICS;
FND_LOG_UNIQUE_EXCEPTIONS;
FND_LOG_EXCEPTIONS;
FND_LOG_MESSAGES;
FND_LOG_TRANSACTION_CONTEXT;
FND_LOG_ATTACHMENTS

These tables contain debug & error messages.

Reference:

How to Purge/Troubleshoot the FND_LOG_MESSAGES table (Doc ID 735138.1)