Re: Improve pg_stat_statements scalability

Hi,

I had to fix an issue with the serialization callback that was causing
CI failures.

I also made re-organized the patches a bit:

v1-0001: This will not be part of the main patchset, but will be be a dependency
for the remaining patches. This is, as mentioned above, an in-transaction flush
required [1]

v1-0002: This now only moves the pg_stat_statements hash to a custom
pgstat kind

v1-0003: This moves the query text file to a DSA + file storage.

v1-0004: Adds new columns to pg_stat_statements_info

[1] https://commitfest.postgresql.org/patch/6781/

--
Sami Imseih
Amazon Web Services (AWS)