Added a unit test for the sql_time_limit_ms option.
To test this, I needed to add a custom SQLite sleep() function. I've added a
simple mechanism to the Datasette class for registering custom functions.
I also had to modify the sqlite_timelimit() function. It makes use of a magic
value, N, which is the number of SQLite virtual machine instructions that
should execute in between calls to my termination decision function.
The value of N was not finely grained enough for my test to work - so I've
added logic that says that if the time limit is less than 50ms, N is set to 1.
This got the tests working.
Refs #95
If someone executes 'select * from table' against a table with a million rows
in it, we could run into problems: just serializing that much data as JSON is
likely to lock up the server.
Solution: we now have a hard limit on the maximum number of rows that can be
returned by a query. If that limit is exceeded, the server will return a
`"truncated": true` field in the JSON.
This limit can be optionally controlled by the new `--max_returned_rows`
option. Setting that option to 0 disables the limit entirely.
Closes#69
Simon Willison