2039810 – Table does not get merged automatically


After a table got renamed it is not merged automatically anymore. This will cause memory increase and query performance gets worse.


Other Terms

HANA, ByD, merge, mergedog,  SFSG_CODELIST_DATA


Reason and Prerequisites

You are running HANA revision 71 to 74.03 or 80 or 81.

After renaming a column store table, the automatic delta merge does not work anymore. The problematic sequence is:

– Create new table TABLE_NEW
– Insert into TABLE_NEW (select * from TABLE_OLD)

This sequence is typically performed during a table conversion initiated from SAP Netweaver ABAP (with intermediate table names QCM<table>, QCM8<table>). Mainly systems running ByD in revision 74 are impacted on table SFSG_CODELIST_DATA.

The result is a large Delta Storage of the Column Store table and a small/empty Main Storage (see monitoring view M_CS_TABLES). The issue can be confirmed by switching on the mergedog trace to trace level INFO. The indexserver trace file contains this message for the problematic table:

i Mergedog         Mergedog.cpp(00619) : TABLE_NEW: table not found, skip auto optimize



As a short term workaround merge the problematic table manually, by running the following command in HANA Studio:

merge delta of TABLE;

Alternatively you may recreate the table:

rename TABLE to TABLE_old
create column table TABLE as ( select * from TABLE_old);

If possible, restart the HANA database. Afterwards the table will be automatically delta merged again.

The problem is solved in SAP HANA revision 74.04 and 82 and later.


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