(Ep. 21) - Db2 REDUCE MAX Command

You have run a REORG on a few of your tables and your data is in a nice contiguous order. What do you do with all the empty data extents? Release them to the operating system so your capacity needs drop of course. Everyone loves seeing your data filesystem drop ftom 70% full to 45% full.
Today we will discuss tablespace watermarks, how Db2 views what space is needed where, and the REDUCE command.
Timestamps:
01:25 - What is a High Watermark
04:31 - Viewing Tablespace Details
05:51 - db2dart (Detail High Water Mark)
08:15 - db2dart (Lower High Watermark)
09:20 - Releasing PENDING free pages
10:34 - REDUCE MAX Command
12:32 - Monitoring Extent Movement
14:22 - REORG vs Export/Import
Download (EXT_STATUS.sql):
github.com/MKrafick/DiscoverDB2
Useful Links:
(KC) Reclaiming unused storage in AST - tinyurl.com/y92wkdta
(KC) Reclaimable Storage (*Good article on Watermarks) - tinyurl.com/ycndehoc
(Blog w/ SQL) Monitoring Extent Movement Progress - tinyurl.com/ybwcpa2n

[@rscarawa]

Is there any performance advantage to leaving the open space in place? Will inserts run faster if you leave the HWM alone?

[@sanjaysinghbora7923]

Isnt db2dart an offline command

[@DISCOVERDB2]

Not necessarily. They highly recommend it because it can lead to false data. It can also be intrusive. But I have run it online before. In some cases like index corruption repair you would definitely want it offline.