One Chunk vs. Many Chunks
Hello All We finally upgraded from 9.21 to 9.40. We are planning to add two 50 GB dbspaces to an instance. There are already many dbspaces in this instance and most are around 50 to 60 GB. One dbspace is 256 GB and we are trying to rearrange the data so we can reduce the size of the big one. If we somewhat reuse the scripts we have for creating the other dbspaces, we will be creating 25 2-GB chunks. However, with 9.4 we can have larger chunks. What are the advantages/disadvantages of fewer, larger chunks as opposed to more, smaller chunks? I know the advantages of more rather fewer dbspaces, but I am unsure of the efficiencies at the chunk level. I realize that smaller chunks can reduce possible extent sizes, depending on the size of the extents we need. As this is a data warehouse, some of the tables are rather large (some are larger than 20 GB). One possible angle on this is that this disk space is RAID 5 SAN. We don't have any say in this so please don't hold it against us (Art). This instance is IDS 9.40.UC4 running under Sun 2.8. Thanks Rob Schmitz
I'd go for few large chunks as it makes life easier for you to overview and manage the chunk files or links. It also reduces the amount of space needed in the ROOT RESERVED PAGES to tarck all the chunks (although this may seem neglectible in terms of disk space) Also, it allows for fewer extents per table , which I think is an advantage. It will reduce the amount of calculation needed to map logical to physical addresses in a table , which may have an effect on cpu load. I don't see any advantages of having many small chunks. There may some which I am not aware off or which I don't consider to be an advantage. Regards Tilman -- Tilman Model-Bosch IBM Data Management Solutions, Informix Advanced Support c\\\\o SAP AG TECHDEV 05 Neurrotstr.16 69190 Walldorf forum.subscriber@iiug.org wrote on 08.07.2005 18:45:52: > Hello All > > We finally upgraded from 9.21 to 9.40. We are planning to add two 50 GB > dbspaces to an instance. There are already many dbspaces in this > instance and most are around 50 to 60 GB. One dbspace is 256 GB and we > are trying to rearrange the data so we can reduce the size of the big > one. > > If we somewhat reuse the scripts we have for creating the other > dbspaces, we will be creating 25 2-GB chunks. However, with 9.4 we can > have larger chunks. What are the advantages/disadvantages of fewer, > larger chunks as opposed to more, smaller chunks? I know the advantages > of more rather fewer dbspaces, but I am unsure of the efficiencies at > the chunk level. I realize that smaller chunks can reduce possible > extent sizes, depending on the size of the extents we need. As this is > a data warehouse, some of the tables are rather large (some are larger > than 20 GB). > > One possible angle on this is that this disk space is RAID 5 SAN. We > don't have any say in this so please don't hold it against us (Art). > > This instance is IDS 9.40.UC4 running under Sun 2.8. > > Thanks > > Rob Schmitz > > >