From 28bdb70be46d3fb3a6f992b3f9f2de1defd85a30 Mon Sep 17 00:00:00 2001
From: Ivan Folgueira Bande <ivansete@status.im>
Date: Sun, 7 Jul 2024 15:57:54 +0200
Subject: [PATCH] postgres_driver: better partition creation without exclusive
 access

---
 .../postgres_driver/postgres_driver.nim       | 45 +++++++++++++++----
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/waku/waku_archive/driver/postgres_driver/postgres_driver.nim b/waku/waku_archive/driver/postgres_driver/postgres_driver.nim
index 516d8d70e3..5793139e22 100644
--- a/waku/waku_archive/driver/postgres_driver/postgres_driver.nim
+++ b/waku/waku_archive/driver/postgres_driver/postgres_driver.nim
@@ -918,7 +918,9 @@ const COULD_NOT_ACQUIRE_ADVISORY_LOCK* = "could not acquire advisory lock"
 proc performWriteQueryWithLock*(
     self: PostgresDriver, queryToProtect: string
 ): Future[ArchiveDriverResult[void]] {.async.} =
-  ## This wraps the original query in a script so that we make sure a pg_advisory lock protects it
+  ## This wraps the original query in a script so that we make sure a pg_advisory lock protects it.
+  ## The purpose of this proc is to protect write queries that might be performed simultaneously
+  ## to the same database, from different store nodes.
   debug "performWriteQueryWithLock", queryToProtect
   let query =
     fmt"""
@@ -947,6 +949,11 @@ proc performWriteQueryWithLock*(
           END $$;
 """
   (await self.performWriteQuery(query)).isOkOr:
+    if error.contains(COULD_NOT_ACQUIRE_ADVISORY_LOCK):
+      ## We don't consider this as an error. Just someone else acquired the advisory lock
+      debug "skip performWriteQuery because the advisory lock is acquired by other"
+      return ok()
+
     debug "protected query ended with error", error = $error
     return err("protected query ended with error:" & $error)
 
@@ -971,22 +978,44 @@ proc addPartition(
 
   let partitionName = "messages_" & fromInSec & "_" & untilInSec
 
+  ## Create the partition table but not attach it yet to the main table
   let createPartitionQuery =
-    "CREATE TABLE IF NOT EXISTS " & partitionName & " PARTITION OF " &
-    "messages FOR VALUES FROM ('" & fromInNanoSec & "') TO ('" & untilInNanoSec & "');"
+    "CREATE TABLE IF NOT EXISTS " & partitionName &
+    " (LIKE messages INCLUDING DEFAULTS INCLUDING CONSTRAINTS);"
 
   (await self.performWriteQueryWithLock(createPartitionQuery)).isOkOr:
     if error.contains("already exists"):
       debug "skip create new partition as it already exists: ", skipped_error = $error
       return ok()
 
-    if error.contains(COULD_NOT_ACQUIRE_ADVISORY_LOCK):
-      debug "skip create new partition because the advisory lock is acquired by other"
-      return ok()
-
-    ## for any different error, just consider it
     return err(fmt"error adding partition [{partitionName}]: " & $error)
 
+  ## Add constraint to the partition table so that EXCLUSIVE ACCESS is not performed when
+  ## the partition is attached to the main table.
+  let constraintName = partitionName & "_by_range_check"
+  let addTimeConstraintQuery =
+    "ALTER TABLE " & partitionName & " ADD CONSTRAINT " & constraintName &
+    " CHECK ( storedAt >= " & fromInNanoSec & " AND storedAt < " & untilInNanoSec & " );"
+
+  (await self.performWriteQueryWithLock(addTimeConstraintQuery)).isOkOr:
+    return err(fmt"error creating constraint [{partitionName}]: " & $error)
+
+  ## Attaching the new created table as a new partition. That does not require EXCLUSIVE ACCESS.
+  let attachPartitionQuery =
+    "ALTER TABLE messages ATTACH PARTITION " & partitionName & " FOR VALUES FROM (" &
+    fromInNanoSec & ") TO (" & untilInNanoSec & ");"
+
+  (await self.performWriteQueryWithLock(attachPartitionQuery)).isOkOr:
+    return err(fmt"error attaching partition [{partitionName}]: " & $error)
+
+  ## Dropping the check constraint as it was only necessary to prevent full scan,
+  ## and EXCLUSIVE ACCESS, to the whole messages table, when the new partition was attached.
+  let dropConstraint =
+    "ALTER TABLE " & partitionName & " DROP CONSTRAINT " & constraintName & ";"
+
+  (await self.performWriteQueryWithLock(dropConstraint)).isOkOr:
+    return err(fmt"error dropping constraint [{partitionName}]: " & $error)
+
   debug "new partition added", query = createPartitionQuery
 
   self.partitionMngr.addPartitionInfo(partitionName, beginning, `end`)