How to influence the priority of column store tables which gets unloaded due to LOW MEMORY
ALTERING UNLOAD PRIORITY OF COLUMN TABLES:
Though in HANA we know that HANA triggers a column table unload when it hits peak memory , and the tables that are unloaded are based on LRU (Least recently used), we still can control this behavior .
During UNLOAD, tables with UNLOAD priority 9 gets thrown out from memory sooner against the tables with unload priority 5 .
Eg: In BW on HANA , all the change log and PSA tables(/BIC/B*) have a default UNLOAD priority of 9 while Active table (/BIC/A*) have unload priority of 5 .
We can also manually alter this behavior .
1.How to modify the default behavior on column table using SQL?
The same can be done with below SQL
ALTER TABLE <SCHEMA_NAME>.<TABLE_NAME >UNLOAD PRIORITY 9;
2.What is the default table priority for any manually column table created ?
The default priority is 5 in HANA for any manually created table, which is why it is important to change this behavior if we are dealing with tables which need not have to stay in memory all the time and remove them from fighting for memory with important tables in HANA.
3.How to find out the table priority of any table in HANA .
This can be found out with the help of
Table name : TABLE
Column name: UNLOAD_PRIORITY
select * from TABLES where TABLE_NAME=’<tale_name>’ and schema_name=’<schema_name>’;
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