Re: Proposal: Conflict log history table for Logical Replication

On Sun, Oct 4, 2026 at 2:31 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
>
> And without fix shared as a v77-0003 [1], this would error out with
> below error[2], I have explained the reason [1]. I have added a
> testcase in 035_conflicts.pl file in v79-0003 patch for this issue.
>

Thanks for the patches. I have resumed reviewing this thread. I think
the size cap added in v79-0002 does not fully prevent the >1GB json
value it is meant to guard against.

In build_index_key_json(), the cap is checked against the stored size
(rawsize), but what actually gets appended is the type's output text,
escaped by escape_json(). In some cases, the output can be far larger
than the storage, and the ratio is not the small factor the comment
atop CONFLICT_MAX_VALUE_SIZE assumes. I have attached a test case to
reproduce the problem. In the test, we use composite types such as:

CREATE TYPE ri_n0 AS (f text);
then
CREATE TYPE ri_n1 AS (f ri_n0);
CREATE TYPE ri_n2 AS (f ri_n1);
... going up to ri_n25.

ri_n25 is then used as the key column of a table.

Then we insert a row whose replica identity is
ROW(...ROW(repeat('"',10))...)::ri_n25. On disk it is stored in this
compact nested form (not the expanded one, ~620 bytes), but in
build_index_key_json(), OidOutputFunctionCall (i.e. record_out)
recurses through all 25 nested levels, to expand the value into its
text form, which grows beyond 800MB, and escaping it then exceeds 1GB.
So durng escape_json() post OidOutputFunctionCall(), apply worker
errors out with:
ERROR: string buffer exceeds maximum allowed length (1073741823 bytes)

I have attached the complete steps to reproduce the issue, as well as
a patch to fix the problem. Please review.

thanks
Shveta