BUFFER-COMPARE on old and new buffer with a LOB field in database write trigger hangs session

Why an ABL OpenEdge client session hangs when performing a BUFFER-COMPARE on an old and new buffer of a table with a LOB field in the database write trigger.

Apr 5, 2017
Knowledge

Title

URL Name

BUFFER-COMPARE-on-old-and-new-buffer-with-CLOB-field-in-database-write-trigger-hangs-session

Article Number

000185302

Environment

Product: OpenEdge Version: 11.6.0, 11.6.1 OS: All supported Operating Systems

Question/Problem Description

When performing a BUFFER-COMPARE on an old and new buffer of a table in the database WRITE trigger, the application hangs if using Shared Memory connection.
When killing the application a record in the database remains locked. This is a totally different record than the record that was being modified via the WRITE trigger.
The record that is locked also contains an LOB field. When performing a FOR EACH xxx NO-LOCK on that specified record, application also hangs.

If using TCP connection, the same code the session does not hang and instead raises error:

"Communication error with server, BLOB compare is unknown. (14497)" .

Why LOB fields from the OLD BUFFER of a write trigger cannot be used for comparison in any version.

Steps to Reproduce

Clarifying Information

Error Message

Defect Number

Defect PSC00346146

Enhancement Number

Cause

LOB fields from the OLD BUFFER of a write trigger cannot be used for comparison. The OLD BUFFER does not contain a before image of any lob data so it is not reliable for determining if a lob column has changed. However the client session should not hang. Instead, the AVM should return an error.

Resolution

Upgrade to OpenEdge 11.6.2 Service Pack, 11.7.0 or later.

The fix for this defect means that the client will no longer hang and the AVM now returns an appropriate error:

"Cannot compare LOB columns from the OLD BUFFER in a WRITE TRIGGER PROCEDURE" .

To allow the code to run as intended, exclude all CLOB fields from the BUFFER-COMPARE statements in the WRITE triggers. For example, to skip BLOB or CLOB fields during BUFFER-COPY and BUFFER-COMPARE, use the NO-LOBS option.

For further clarification refer to Article:

Error 16683 trying to access a BLOB or CLOB field value in write trigger OLD BUFFER

Workaround

Notes

Progress Article:

Error with SAVE-ROW-CHANGES saving buffers with CLOB & BLOB fields

Keyword Phrase

Last Modified Date

11/20/2020 7:16 AM

BUFFER-COMPARE on old and new buffer with a LOB field in database write trigger hangs session

Files(0)

Was this article helpful?

Was this article helpful?

BUFFER-COMPARE on old and new buffer with a LOB field in database write trigger hangs session

Information

Related Articles