QSqlDatabase db = logDb();
+ // TODO: For databases that support it (e.g. almost only PostgreSQL), wrap upgrades in a
+ // transaction. This will need careful testing of potential additional space requirements and
+ // any database modifications that might not be allowed in a transaction.
+
for (int ver = installedSchemaVersion() + 1; ver <= schemaVersion(); ver++) {
foreach(QString queryString, upgradeQueries(ver)) {
QSqlQuery query = db.exec(queryString);
if (!watchQuery(query)) {
- qCritical() << "Unable to upgrade Logging Backend!";
+ // Individual upgrade query failed, bail out
+ qCritical() << "Unable to upgrade Logging Backend! Upgrade query in schema version"
+ << ver << "failed.";
return false;
}
}
+
+ // Update the schema version for each intermediate step. This ensures that any interrupted
+ // upgrades have a greater chance of resuming correctly after core restart.
+ //
+ // Almost all databases make single queries atomic (fully works or fully fails, no partial),
+ // and with many of the longest migrations being a single query, this makes upgrade
+ // interruptions much more likely to leave the database in a valid intermediate schema
+ // version.
+ if (!updateSchemaVersion(ver)) {
+ // Updating the schema version failed, bail out
+ qCritical() << "Unable to upgrade Logging Backend! Setting schema version"
+ << ver << "failed.";
+ return false;
+ }
}
- return updateSchemaVersion(schemaVersion());
+
+ // Update the schema version for the final step. Split this out to offer more informative
+ // logging (though setting schema version really should not fail).
+ if (!updateSchemaVersion(schemaVersion())) {
+ // Updating the final schema version failed, bail out
+ qCritical() << "Unable to upgrade Logging Backend! Setting final schema version"
+ << schemaVersion() << "failed.";
+ return false;
+ }
+
+ // If we made it here, everything seems to have worked!
+ return true;
}