On Sat, Sep 30, 2023 at 11:37 PM Tom Lane <t...@sss.pgh.pa.us> wrote:
> James Healy <ja...@yob.id.au> writes: > > However it doesn't really address the question of a gradual migration > > process that can read 32bit ints but insert/update as 64bit bigints. I > > remain curious about whether the postgres architecture just makes that > > implausible, or if it could be done and just hasn't because the > > options for a more manual migration are Good Enough. > > I think what you're asking for is a scheme whereby some rows in a > table have datatype X in a particular column while other rows in > the very same physical table have datatype Y in the same column. > That is not happening, because there'd be no way to tell which > case applies to any particular row. > Other databases do allow that sort of gradual migration. One example has an internal table of record descriptions indexed the table identifier and a description number. Each record includes a header with various useful bits including its description number. When reading a record, the system notes the description number and looks up the description before parsing the record into columns. The transition is made easier if the database indexes are generic - for example, numbers rather than decimal[12,6], int32, etc., and string rather than varchar[12]. That way, increasing a column size doesn't require re-indexing. But, those are decision that really had to be made early - making a major format change 25+ years in would break too much. Cheers, Ann > > > > >
