> > > Add a new option to force index recreation in vacuum
> > > and if index recreation is specified.
> >
> > Couldn't we auto-recreate indexes based on the number of tuples moved by
> > vacuum,
>
> Yes,we could probably do it. But I'm not sure the availability of new
> vacuum.
>
> New vacuum would give us a big advantage that
> 1) Much faster than current if vacuum remove/moves many tuples.
> 2) Does shrink index files
>
> But in case of abort/crash
> 1) couldn't choose index scan for the table
> 2) unique constraints of the table would be lost
>
> I don't know how people estimate this disadvantage.
That's why I was recommending rename(). The actual window of
vunerability goes from perhaps hours to fractions of a second.
In fact, if I understand this right, you could make the vulerability
zero by just performing the rename as one operation.
In fact, for REINDEX cases where you don't have a lock on the entire
table as you do in vacuum, you could reindex the table with a simple
read-lock on the base table and index, and move the new index into place
with the users seeing no change. Only people traversing the index
during the change would have a problem. You just need an exclusive
access on the index for the duration of the rename() so no one is
traversing the index during the rename().
Destroying the index and recreating opens a large time span that there
is no index, and you have to jury-rig something so people don't try to
use the index. With rename() you just put the new index in place with
one operation. Just don't let people traverse the index during the
change. The pointers to the heap tuples is the same in both indexes.
In fact, with WAL, we will allow multiple physical files for the same
table by appending the table oid to the file name. In this case, the
old index could be deleted by rename, and people would continue to use
the old index until they deleted the open file pointers. Not sure how
this works in practice because new tuples would not be inserted into the
old copy of the index.
-- Bruce Momjian | http://www.op.net/~candle pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
