Re: Keeping state in a foreign data wrapper

On 2020/08/04 19:21, Stelios Sfakianakis wrote:
> Thank you again, I have another question in order to make sure I have a clear understanding:
>
>
>> On 4 Aug 2020, at 11:24, Ian Lawrence Barwick <barwick(at)gmail(dot)com> wrote:
>>
>> The hash table is specific to each running backend so will only be
>> accessed by that process.
>>
>> Pre-loading a shared library just gives the library an opportunity to
>> set up shared memory etc. You can always try adding one of the FDW
>> libraries to "shared_preload_libraries" and see what happens
>> (theoretically nothing).
>>
>
> My impression was that since each client (e.g. libpq) connection results in the creation of a Postgres process in the backend (https://www.postgresql.org/developer/backend/) then this (mysql) "connection pool" hash table is not global per se and shared among the different client / users sessions.

Correct, the connections are specific to each individual backend.

> But that defeats the purpose, no?

The purpose is to cache connections within the session, to avoid the overhead
of reconnecting to the remote server each time a query for that server is issued
in that session.

Regards

Ian Barwick

--
Ian Barwick https://www.2ndQuadrant.com/
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