From d47e4a2a4148ff0b6467d5bda504401b90bb00da Mon Sep 17 00:00:00 2001
From: Konstantin Knizhnik <knizhnik@garret.ru>
Date: Thu, 11 Apr 2024 07:47:45 +0300
Subject: [PATCH] Remember last written LSN when it is first requested (#7343)

## Problem

See https://neondb.slack.com/archives/C03QLRH7PPD/p1712529369520409

In case of statements CREATE TABLE AS SELECT... or INSERT FROM SELECT...
we are fetching data from source table and storing it in destination
table. It cause problems with prefetch last-written-lsn is known for the
pages of source table
(which for example happens after compute restart). In this case we get
get global value of last-written-lsn which is changed frequently as far
as we are writing pages of destination table. As a result request-isn
for the prefetch and request-let when this page is actually needed are
different and we got exported prefetch request. So it actually disarms
prefetch.


## Summary of changes

Proposed simple patch stores last-written LSN for the page when it is
not found. So next time we will request last-written LSN for this page,
we will get the same value (certainly if the page was not changed).

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
---
 vendor/postgres-v14   | 2 +-
 vendor/postgres-v15   | 2 +-
 vendor/postgres-v16   | 2 +-
 vendor/revisions.json | 6 +++---
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/vendor/postgres-v14 b/vendor/postgres-v14
index a7b4c66156..d9149dc59a 160000
--- a/vendor/postgres-v14
+++ b/vendor/postgres-v14
@@ -1 +1 @@
-Subproject commit a7b4c66156bce00afa60e5592d4284ba9e40b4cf
+Subproject commit d9149dc59abcbeeb26293707509aef51752db28f
diff --git a/vendor/postgres-v15 b/vendor/postgres-v15
index 64b8c7bccc..85d809c124 160000
--- a/vendor/postgres-v15
+++ b/vendor/postgres-v15
@@ -1 +1 @@
-Subproject commit 64b8c7bccc6b77e04795e2d4cf6ad82dc8d987ed
+Subproject commit 85d809c124a898847a97d66a211f7d5ef4f8e0cb
diff --git a/vendor/postgres-v16 b/vendor/postgres-v16
index 3946b2e2ea..261497dd63 160000
--- a/vendor/postgres-v16
+++ b/vendor/postgres-v16
@@ -1 +1 @@
-Subproject commit 3946b2e2ea71d07af092099cb5bcae76a69b90d6
+Subproject commit 261497dd63ace434045058b1453bcbaaa83f23e5
diff --git a/vendor/revisions.json b/vendor/revisions.json
index 75dc095168..dfc0aa04c3 100644
--- a/vendor/revisions.json
+++ b/vendor/revisions.json
@@ -1,5 +1,5 @@
 {
-  "postgres-v16": "3946b2e2ea71d07af092099cb5bcae76a69b90d6",
-  "postgres-v15": "64b8c7bccc6b77e04795e2d4cf6ad82dc8d987ed",
-  "postgres-v14": "a7b4c66156bce00afa60e5592d4284ba9e40b4cf"
+  "postgres-v16": "261497dd63ace434045058b1453bcbaaa83f23e5",
+  "postgres-v15": "85d809c124a898847a97d66a211f7d5ef4f8e0cb",
+  "postgres-v14": "d9149dc59abcbeeb26293707509aef51752db28f"
 }