Re: Alter Table on 41 million rows (2G):

sujata_soman_at_omm-la2-infotech-001@internet.omm.com wrote: > > Hi all, > Background Info : Informix ver 7.22 UC4, HP-UX 10.20. > I need to alter a table which has about 41 million rows ( 2Gig data ), > basically changing the data type of one single column. This table has 40 > fragments ( don't ask me why ) > My question is as follows:- > a. What are the factors that influence the performance of this query ? Disk speed and PDQPRIORITY and version (7.3 will be able to do this in-place and versions before 7.2x used a less efficient ALTER TABLE algorithm. > b. What do I to speed up the process ? PDQPRIORITY=75 > c. How does setting it as a PDQ process compare it to running it as a normal > process with PSORT_NPROCS set to an appropriate value PSORT_NPROCS only affects sorts and index builds (because of the inherent sort). > d. Would running the query generate 40 parallel session ( for 40 fragments > ), or do I have to force it in some way ? If PDQPRIORITY > 1 then yes otherwise fragments will be copied in series. Higher PDQ priority will allow more concurrency by allowing more threads to be active. BTW you know that each DBSPACE will need AT LEAST as much free space as it currently uses for the reorg since this is accomplished by creating a new identical table with the new column type and copying data from the old table then drop the old table. If you do not have enough space in the current 40 DBSPACES it might be better to create a new table in 40 other dbspaces, copy the data, drop the old table, rename the new table. Art S. Kagel