Calculating First Extent Size

Posted in 1999

Bonnie Annelin — Thu, 28 Oct 1999 16:49:37 -0700 — source: Informix-list mailing list archive (1991-1998)

Hi - Can anyone help me with the following... I am using the Informix recommend calculation to determine the size to use for first extent of a table: useable page size = 2048 (size of our page) - 28 bytes overhead = 2020 bytes rows per page = rounddown (useable page size / (rowsize + 4 )) First Extent (in pages) = roundup (# rows expected / rows per page) First Extent (in kilobytes) = # pages * 2 (2kb = page size of machine) However...I noticed that this calculation doesn't seem to take into account the number of pages required for bitmap pages. Therefore, in some cases, I'm needing to use the next extent. Can anyone shed any light on this? Thanks, Bonnie Annelin Intuit, Inc.

↪ replying to Bonnie Annelin

Yuri Dovgart — Fri, 5 Nov 1999 10:17:50 +0300 — source: Informix-list mailing list archive (1991-1998)

Usually you don't need to take bitmaps into account. 4-bit bitmap pages arrives 1 time per ~ 8500 pages. If you want to calcute exact number of pages for your table, take them into account. But formula above looks good for tables without grows. If your tables are expexted to be growing, the only way to determine extent size is permanently monitor table. ------------------------------------------------- With best regards, Yuri Dovgart SAP R/3, Informix technical consultant, Senior System Consultant System Architecture and High Availability Systems, 'Telecominvest' company Email y_dovgart@tci.ukrtel.net ICQ 39284285 Bonnie Annelin <bonnie_annelin@intuit.com> wrote in message news:3818E111.431480E4@intuit.com... > Hi - > > Can anyone help me with the following... > > I am using the Informix recommend calculation to determine the size to > use for first extent of a table: > > useable page size = 2048 (size of our page) - 28 bytes overhead = 2020 > bytes > rows per page = rounddown (useable page size / (rowsize + 4 )) > First Extent (in pages) = roundup (# rows expected / rows per page) > First Extent (in kilobytes) = # pages * 2 (2kb = page size of machine) > > However...I noticed that this calculation doesn't seem to take into > account the number of pages required for bitmap pages. Therefore, in > some cases, I'm needing to use the next extent. > > Can anyone shed any light on this? > > Thanks, > Bonnie Annelin > Intuit, Inc. > > > >