Re: Wraparound

So, is there a way to change to 64bit?

On Wed, 21 Feb 2024, 13:55 Vijaykumar Jain, <vijaykumarjain(dot)github(at)gmail(dot)com>
wrote:

> this might help explain what laurenz tried to put in words.
> although this is actual wraparound trigger when db will be blocked for
> activity but helps understand the setup, hopefully.
>
> https://tuple-freezing-demo.angusd.com/
>
> On Tue, Feb 20, 2024, 1:12 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
> wrote:
>
>> On Tue, 2024-02-20 at 12:57 +0530, Rajesh Kumar wrote:
>> > On Tue, 20 Feb 2024, 12:53 Laurenz Albe, <laurenz(dot)albe(at)cybertec(dot)at>
>> wrote:
>> > > On Tue, 2024-02-20 at 10:02 +0530, Rajesh Kumar wrote:
>> > > > Is autovacuum wraparound issue is when transaction id reaches
>> > > > autovacuum_freeze_max_age or if transaction Reaches 2^32.
>> > > >
>> > > > My autovacuum_freeze_age setting is 200million.
>> > > >
>> > > > Db size is 150gb.
>> > >
>> > > 2^31 is the magical number at which very old transactions become
>> > > transactions from the future, which would cause data loss unless
>> > > all old rows have been frozen.
>> >
>> > Sorry, I could not understand. If possible, please elaborate.
>> Otherwise, no issues
>>
>> The (32-bit) transaction numbers are stored in "xmin" and "xmax" in each
>> row.
>> You have to imagine these numbers as a closed ring: if you get past
>> 2^32-1,
>> you wrap around to 0 and continue.
>>
>> Now the 2^31 numbers before the current 32-bit transaction id are the
>> past,
>> and the 2^31 numbers after it are the future. This includes wraparound,
>> so
>> initially numbers close to 2^32 will also be past.
>>
>> As the current transaction id crosses 2^31, very old transactions suddenly
>> become future transactions. All rows with a low "xmin" will suddenly
>> appear
>> to have been created in the future and become invisible. Some rows with a
>> low "xmax" that have been deleted long ago can suddenly rise from the
>> dead,
>> since the transaction that deleted them now appears to be in the future.
>>
>> Perhaps you will find this article entertaining:
>>
>> https://www.cybertec-postgresql.com/en/transaction-id-wraparound-a-walk-on-the-wild-side/
>>
>> Yours,
>> Laurenz Albe
>>
>>
>>