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Status Future consideration
Workspace Db2
Created by Guest
Created on Sep 1, 2020

Allow table compression to be disabled for DGTTs and CGTTs

In short: OLTP applications frequently encounter performance issues because DB2 enables table compression by default for all DGTTs / CGTTs.

Details from a real-time example:

When inserting 40K rows to a DGTT, it takes 2 seconds.

When we immediately insert another 40K rows to the same DGTT using the same INSERT statement, it takes 0.08 seconds.

This has nothing to do with caching. It is because compression is enabled by default for all DGTTs / CGTTs and this is the overhead of generating the compression dictionary.

DB2 only generates the compression dictionary if a certain amount of data is inserted (based on my tests, this was around 25K rows). The same applies to CGTTs.

What this means is that any proc which inserts > 25K rows (approx.) into a DGTT / CGTT will incur this significant overhead every time it is executed.

So procs that should take 0.08 seconds to execute will consistently take 2 seconds.

Most OLTP applications create small (and short-lived) temporary tables and therefore don't benefit from table compression. Having the ability to disable table compression will significantly improve query performance in many cases.

Needed by Date Dec 31, 2020