Re: Detached indices in 7.3

SaTriGuy wrote: . . . snip . . . > In the 4.x and 5.x days, the concept of including the index pages within the > same tablespace as the datapages was a performance argument. The theory was > that if the disk head was close to the data then there would be little head > motion between the reading of the index pages and the actual data page. Nice > theory but not factual in multi-use environments because by the time the index > had been read, some other user would have already moved the head. > Makes sense. > By making the indexes detached we are able to maximize read-aheads. This means > that when we are reading datapages, we don't have to skip over index pages, > simply read. This minimizes disk head motion during scan phases and maximizes > the useful data read by sequential reads. > I thought that Informix didn't skip pages; hence, the ixda-RA portion of onstat -p. > As far as this approach taking more space, - nope right the opposite. The data > extent should contain the same number of data pages as before and the index > extent should contain the index pages. There should be no difference in the > total number of pages used. > Other than extents, yes. > From a maintenance standpoint, attached indexes are still functional. I just > ran a quick test on 7.3 and my index was still attached. If this behaves like > 9.x, then attached indexes can still be used, so the user does not have to drop > and recreate their indexes. However with 9.x, any new indexes will be > detached, even though they are in the same dbspace. So then any changes would be in a much-later release? That makes more sense.