murmur database write performance

[ailox]

When issuing multiple concurrent requests that are persisted in the database, the server will become sluggish. This seemed to be the reason for the crashes in issue #3505 , which is now simply masked by the rate limiting.

From what I can tell these problems exist

• when writing (INSERT-ing or UPDATE-ing to the database)
• with the default QSQLITE driver
• with the QMYSQL driver
• with QSQLITE in memory (':memory:').

It therefore seems to me like the bottleneck lies before the database driver code.