Re: Potential data loss due to race condition during logical replication slot creation

On Wed, Jul 10, 2024 at 7:52 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> Overall I think the patches are in good shape, so I'm going to push
> them tomorrow, barring any objections and further comments.
>

Agreed. Below are a few minor comments that you might want to consider:

1.
@@ -76,6 +77,7 @@ extern SnapBuildState
SnapBuildCurrentState(SnapBuild *builder);
extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder);

extern bool SnapBuildXactNeedsSkip(SnapBuild *builder, XLogRecPtr ptr);
+extern void SnapBuildSetFindStartPoint(SnapBuild *builder, bool
find_start_point);

This is not required in the latest version.

2.
+ /*
+ * Indicates if we are using the snapshot builder for the initial creation
+ * of a logical replication slot.

The word 'initial' in the above comment is not required. If you
consider this then a similar wording change is required in lower
branches as well.

3.
HEAD and v17
---------------------
- /* b) valid on disk state and not building full snapshot */
+
+ /*
+ * b) valid on disk state and while neither building full snapshot nor
+ * finding the start point.
+ */
else if (!builder->building_full_snapshot &&
+ !builder->in_slot_creation &&

V16 and below
---------------------
- /* b) valid on disk state and not building full snapshot */
+
+ /*
+ * b) valid on disk state and neither building full snapshot nor while
+ * creating a slot.
+ */
else if (!builder->building_full_snapshot &&
+ !ctx->in_create &&

Isn't it better to use the same comment in both places?

--
With Regards,
Amit Kapila.