From 0a6e837aaadec0342f31f29c48800f5ce5e3531b Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Wed, 27 May 2020 16:26:59 +0100
Subject: [PATCH] Fix incorrect placeholder syntax in database prepartion code
 (#7575)

We were using `logger` syntax which isn't supported by `Exception`s.
---
 changelog.d/7575.bugfix             | 1 +
 synapse/storage/prepare_database.py | 5 ++---
 2 files changed, 3 insertions(+), 3 deletions(-)
 create mode 100644 changelog.d/7575.bugfix

diff --git a/changelog.d/7575.bugfix b/changelog.d/7575.bugfix
new file mode 100644
index 000000000..0ab5516eb
--- /dev/null
+++ b/changelog.d/7575.bugfix
@@ -0,0 +1 @@
+Fix str placeholders in an instance of `PrepareDatabaseException`. Introduced in Synapse v1.8.0.
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 9afc14534..b95434f03 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -366,9 +366,8 @@ def _upgrade_existing_database(
         if duplicates:
             # We don't support using the same file name in the same delta version.
             raise PrepareDatabaseException(
-                "Found multiple delta files with the same name in v%d: %s",
-                v,
-                duplicates,
+                "Found multiple delta files with the same name in v%d: %s"
+                % (v, duplicates,)
             )
 
         # We sort to ensure that we apply the delta files in a consistent