Re-land https://codereview.chromium.org/2108563002/

third_party/buildbot_8_4p1/buildbot/db/pool.py

Index: third_party/buildbot_8_4p1/buildbot/db/pool.py
diff --git a/third_party/buildbot_8_4p1/buildbot/db/pool.py b/third_party/buildbot_8_4p1/buildbot/db/pool.py
index 6b2a1d870d09523e9896dc89c09d9b4beb49f2d6..e1141e453cd32df6f3771174d4bbd739ee3b2a95 100644
--- a/third_party/buildbot_8_4p1/buildbot/db/pool.py
+++ b/third_party/buildbot_8_4p1/buildbot/db/pool.py
@@ -71,6 +71,10 @@ class DBThreadPool(threadpool.ThreadPool):
         if engine.dialect.name == 'sqlite':
             vers = self.get_sqlite_version()
             log.msg("Using SQLite Version %s" % (vers,))
+            if vers < (3,7):
+                log.msg("NOTE: this old version of SQLite does not support "
+                        "WAL journal mode; a busy master may encounter "
+                        "'Database is locked' errors.  Consider upgrading.")
             if vers < (3,3,17):
                 log.msg("NOTE: this old version of SQLite does not support "
                         "multiple simultaneous accesses to the database; "