On 14/09/14 05:36, Rohit Goyal wrote:
Hi All,

I want to work on the code of intermediate dataset of select and update

For example.

Rohit's salary has been updated 4 times, so it has 4 different version
of salary.

I want to select  salary of person named Rohit. Now suppose , in
intermediate result, I found 4 different versions of the data. I want to
know the code portion which i need to look for working on all 4 versions
in dataset. :)

Hi Rohit,

Currently in Postgres, these intermediate versions all exist - however a given session can only see one of them. Also VACUUM is allowed to destroy versions that no other transactions can see.

So if I'm understanding you correctly, you would like to have some way for a session to see *all* these versions (and I guess preventing VACUUM from destroying them).

It is certainly possible (or used to be via snapshot manipulation, I haven't looked at that code in a while sorry) to enable a session to see all the old versions, and is quite a cool idea (Postgres used to have this ability in older versions - called Time Travel).

For pure practicality, this can be achieved without any code modifications using TRIGGERs and an extra table (as Gavin alludes to).

Do tell us a bit more about what you are wanting to do!



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