Re: psql backward compatibility

On 11/18/20 10:13 AM, Adrian Klaver wrote:
> On 11/18/20 8:05 AM, Stephen Haddock wrote:
>> Hello,
>>
>> When upgrading an older version of postgres, version 8.4 for example, to 
>> a newer version such as 9.6, does the data have to be migrated immediately?
>>
>> It looks like the recommended method is to dump the data, upgrade, 
>> initialize a new cluster, and then restore the dumped data into the newer 
>> version. My question is whether the data dump and restore must be done 
>> immediately. It appears that 9.6 is able to run against the older cluster 
>> (DB service starts, queries work, etc), and the data could be migrated 
>> days or weeks later. I don't know if that is asking for issues down the 
>> line though such as 9.6 corrupting the data due to incompatibilities 
>> between the two versions.
>
> https://www.postgresql.org/docs/9.6/app-pgdump.html
>
> "Because pg_dump is used to transfer data to newer versions of PostgreSQL, 
> the output of pg_dump can be expected to load into PostgreSQL server 
> versions newer than pg_dump's version. pg_dump can also dump from 
> PostgreSQL servers older than its own version. (Currently, servers back to 
> version 7.0 are supported.) "
>
>
> The above is for Postgres 9.6 version of pg_dump. Newer versions(10+) go 
> back to Postgres 8.0.  You can dump the old server at anytime. The 
> important thing to remember is to dump the old server using the new 
> servers version of pg_dump. So in your case pg_dump(9.6) against server(8.4).

This is especially useful, since the 9.6 pg_dump is able to do parallel 
operations against 8.4.

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