Re: What's the best practice to compare the transaction with the checkpoint?

Actually I am trying to add file support for TOAST. I mean store the
toasted value in the file system and leave a file path in the toast
pointer. Therefore, for garbage collection, we need to remove the file
after confirming that a deleted tuple is older than the latest checkpoint.

Thanks,
JIalun Zhang

Gerald Cheves <gcheves(at)verizon(dot)net> 于2020年7月6日周一 上午10:58写道：

> On 7/6/2020 10:09 AM, Jialun Zhang wrote:
>
> Thanks! But what I actually mean is how to do this in the backend source
> code. I think I could find a way to do this SELECT in backend.
>
> What would be the advantage in that method?
>
>
> Thank you,
> Jialun Zhang
>
> Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> 于2020年7月6日周一 上午4:09写道：
>
>> On Sat, 2020-07-04 at 12:19 -0400, Jialun Zhang wrote:
>> > I am trying to add code to determine whether the transaction is
>> checkpointed or not.
>> > So I think I need to compare the transaction ID with the checkpoint's
>> and determine
>> > whether it is older or not. Could anyone tell me what's the best
>> practice of doing
>> > this in Postgres? Is it done somewhere in the existing code?
>>
>> You could use
>>
>> SELECT next_xid FROM pg_control_checkpoint();
>>
>> to get information about the last checkpoint.
>>
>> I refrain from asking what the point of the exercise is...
>>
>> Yours,
>> Laurenz Albe
>> --
>> Cybertec | https://www.cybertec-postgresql.com
>>
>>
> --
> siamo arrivati sani e salvi
>
>