Does Write-Ahead-Logging allow me to make concurrent changes to a table? In Sqlite3, Write-Ahead-Logging mode allows one process to read a table, while another is writing to it. It doesn't say anything about one process writing and another deleting/updating.

Is this possible in Sqlite3?
A DELETE and/or an UPDATE are both writes! 

Only one process can write at any one time - that is an INSERT, an UPDATE or a DELETE at the same time. You can SELECT with as many processes as you like, but only one of the others at a time!