On 2 Nov 2015, at 3:48am, sanhua.zh <sanhua.zh at foxmail.com> wrote:
> I thought it might be storage contention, too. > BUT, as the documentation of SQLite said, in ?DELETE? mode, SELECTing do read > for disk only. Even reading needs the attention of the disk. You tell the disk what you want to read and it has to find that piece of disk, read it, and give the result to you. It cannot answer four requests at once so while it's answering one, the other threads have to wait. (Yes disk is cached. But that just moves the problem from the hard disk to the piece of software which handles the cache. It cannot answer four questions at once.) Simon.
