[CALCITE-849] Streams/Slow iterators dont close on statement close

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Jesse Yates
• Created: 19/Aug/15 23:18
• Updated: 22/Feb/19 01:19

Description

This is easily seen when querying an infinite stream with a clause that cannot be matched

select stream PRODUCT from orders where PRODUCT LIKE 'noMatch';
select stream * from orders where PRODUCT LIKE 'noMatch';

The issue arises when accessing the results in a multi-threaded context. Yes, its not a good idea (and things will break, like here). However, this case feels like it ought to be an exception.

Suppose you are accessing a stream and have a query that doesn't match anything on the stream for a long time. Because of the way a ResultSet is built, the call to executeQuery() will hang until the first matching result is received. In that case, you might want to cancel the query because its taking so long. You also want the thing that's accessing the stream (the StreamTable implementation) to cancel the querying/collection - via a call to close on the passed iterator/enumerable.

Since the first result was never generated, the ResultSet was never returned to the caller. You can get around this by using a second thread and keeping a handle to the creating statement. When you go to close that statement though, you end up not closing the cursor (and the underlying iterables/enumberables) because it never finished getting created.

It gets even more problematic if you are use select * as the iterable doesn't finish getting created in the AvaticaResultSet.

Issue Links

• depends upon: CALCITE-809 TableScan does not support large/infinite scans
• relates to: CALCITE-1227 Add streaming CSV table