Re: Proposal: Conflict log history table for Logical Replication

On Sun, Aug 30, 2026 at 8:43 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Wed, Aug 26, 2026 at 8:01 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> Updated version of 0002, based on offlist testing by Nisha, revealed
> that the assumption that a column's maximum size could become 6x its
> original size during JSON conversion is incorrect. One edge case is a
> column of type array (int[]). A huge array but mostly empty(all NULL),
> can have a small storage size but produce a much larger JSON since
> each element is serialized. For example
> - A 4096 byte text column becomes ~24KB json (6x), which stays under
> the budget even accumulated across all columns (24,554 × 1600 × 3 ≈
> 118 MB).
> - But a 4096 byte all-NULL int[] column can produce ~480KB(120x) of
> json in a edge case.
> Based on this, Amit suggested a offlist POC of the patch which Nisha
> and I further modified. It still needs more review, testing, and logic
> validation, but I am sharing it here so we can review and provide
> feedback.
>

Thanks. I found an issue where worker-statics size-limit flags cause
re-entrant inner JSON operations to prematurely trigger the limit,
resulting in false-positive column omissions. This is demonstrated in
the attached test.

This can be addressed by saving the size-limits before invoking
internal type and cast related functions. I've attached the patch.

thanks
Shveta