BRIN: Prevent the heapblk overflow during index summarization on very large tables resulting in an infinite loop

Previously, *heapBlk* was defined as an unsigned 32-bit integer. When
incremented

by *pagesPerRange *on very large tables, it could wrap around, causing the
condition

*heapBlk < nblocks* to remain true indefinitely — resulting in an *infinite
loop*.

This could cause the PostgreSQL backend to hang, consuming 100% CPU
indefinitely

and preventing operations from completing on large tables.

The solution is straightforward — the data type of `heapBlk` has been
changed

from a 32-bit integer to a 64-bit `BlockNumber` (int64), ensuring it can
safely

handle extremely large tables without risk of overflow.

This was explained very nicely by Tomas Vondra[1] and below two solutions
were

suggested.

i) Change to int64

ii) Tracking the prevHeapBlk

Among these two I feel using solution #1 would be more feasible(similar to
previously used solution 4bc6fb57f774ea18187fd8565aad9994160bfc17[2]),
though

other solution also works.

I’ve attached a patch with the changes for *solution #1*.
Kindly review it and share your feedback or suggestions — your input would
be greatly appreciated.

Reference:

[1]
https://www.postgresql.org/message-id/b8a4e04c-c091-056c-a379-11d35c7b2d8d%40enterprisedb.com

[2]
https://github.com/postgres/postgres/commit/4bc6fb57f774ea18187fd8565aad9994160bfc17

Thanks & Regards,
Sunil Seetharama
Broadcom Inc