sqlite: disable WAL mode

Disable the write-ahead log [1] for sqlite.  Performance testing
suggests that WAL mode has a negative impact on Podman.  While most docs
suggest that WAL mode improves performance, it does not seem to apply to
Podman which tends to have very short-lived processes.

What I found most curious is that commands with many writes are faster
without WAL mode, for instance, `rm`, `stop`, `start`, etc.

Hence, let's move to as-close-to-default config of sqlite and enable
options only after thorough testing.

[NO NEW TESTS NEEDED] as it's a non-functional change.

[1] https://www.sqlite.org/wal.html

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

libpod/sqlite_state.go

@@ -32,10 +32,6 @@ type SQLiteState struct {
 const (
 	// Deal with timezone automatically.
 	sqliteOptionLocation = "_loc=auto"
-	// Set the journal mode (https://www.sqlite.org/pragma.html#pragma_journal_mode).
-	sqliteOptionJournal = "&_journal=WAL"
-	// Force WAL mode to fsync after each transaction (https://www.sqlite.org/pragma.html#pragma_synchronous).
-	sqliteOptionSynchronous = "&_sync=FULL"
 	// Allow foreign keys (https://www.sqlite.org/pragma.html#pragma_foreign_keys).
 	sqliteOptionForeignKeys = "&_foreign_keys=1"
 	// Make sure that transactions happen exclusively.
@@ -44,8 +40,6 @@ const (
 	// Assembled sqlite options used when opening the database.
 	sqliteOptions = "db.sql?" +
 		sqliteOptionLocation +
-		sqliteOptionJournal +
-		sqliteOptionSynchronous +
 		sqliteOptionForeignKeys +
 		sqliteOptionTXLock
 )