[OE-core] [RFC v2 04/16] bitbake: persist_data: Enable Write Ahead Log

[Joshua Watt]

Enabling the write ahead log improves database reliability, speeds up
writes (since they mostly happen sequentially), and speeds up readers
(since they are no longer blocked by most write operations). The
persistent database is very read heavy, so the auto-checkpoint size is
reduced from the default (usually 1000) to 100 so that reads remain
fast.

Signed-off-by: Joshua Watt <JPEWhacker at gmail.com>
---
 bitbake/lib/bb/persist_data.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/bitbake/lib/bb/persist_data.py b/bitbake/lib/bb/persist_data.py
index 2bc3e766a93..9a4e7dd5941 100644
--- a/bitbake/lib/bb/persist_data.py
+++ b/bitbake/lib/bb/persist_data.py
@@ -278,7 +278,12 @@ class PersistData(object):
 
 def connect(database):
     connection = sqlite3.connect(database, timeout=5)
-    connection.execute("pragma synchronous = off;")
+    connection.execute("pragma synchronous = normal;")
+    # Enable WAL and keep the autocheckpoint length small (the default is
+    # usually 1000). Persistent caches are usually read-mostly, so keeping
+    # this short will keep readers running quickly
+    connection.execute("pragma journal_mode = WAL;")
+    connection.execute("pragma wal_autocheckpoint = 100;")
     connection.text_factory = str
     return connection
 
-- 
2.17.1