test: fix busy replication slot test

The test's intention was to spawn a reader of the replication and ensure
that Materialize can successfully reclaim it by killing the appropriate
server process.

However, the WAL reader that we spawned also advanced the slot forward
without Materialize having seen and committed that section. To avoid
this we pass an extremely long fsync-interval parameter that will result
in the slot being busy but not advanced.

Fixes MaterializeInc/database-issues#8447

Signed-off-by: Petros Angelatos <[email protected]>

Author: petrosagg

test/pg-cdc-old-syntax/mzcompose.py

@@ -57,6 +57,12 @@ def __init__(self, replication_slot_name: str, publication_name: str) -> None:
             f"{replication_slot_name}",
             "--file",
             "-",
+            # We pass the maximum allowed fsync-interval (~24 days) to prevent
+            # this process from advancing the slot. The purpose of this reader
+            # is to just mark the slot as busy, not to move its reserved WAL
+            # forward.
+            "--fsync-interval",
+            "2147483",
             "--dbname",
             "postgres",
             "--host",

test/pg-cdc/mzcompose.py

@@ -50,6 +50,12 @@ def __init__(self, replication_slot_name: str, publication_name: str) -> None:
             f"{replication_slot_name}",
             "--file",
             "-",
+            # We pass the maximum allowed fsync-interval (~24 days) to prevent
+            # this process from advancing the slot. The purpose of this reader
+            # is to just mark the slot as busy, not to move its reserved WAL
+            # forward.
+            "--fsync-interval",
+            "2147483",
             "--dbname",
             "postgres",
             "--host",