MON$-tables are unavaliable when optimizer prepares to execute query with lot
of windowed functions
---------------------------------------------------------------------------------------------------
Key: CORE-4292
URL: http://tracker.firebirdsql.org/browse/CORE-4292
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 3.0 Alpha 1
Reporter: Pavel Zotov
Consider two complex queries - see attach.
Script "prepare_too_long_and_hangs_monitoring.sql" contains a lot of calls to
windowed functions and script "also_complex_but_NOT_trouble_in_preparing.sql"
has no such calls but contains lot of scalar subqueries (in places where
windowed functions were in first one).
The following scenario illustrates what there will be if we try to get
execution plan of both queries.
session #1
=========
C:\1Install\fb30>isql localhost/3330:empty30 -n
Database: localhost/3330:empty30
SQL>
session #2
=========
C:\1Install\fb30>isql localhost/3330:empty30 -n
Database: localhost/3330:empty30
SQL> in prepare_too_long_and_hangs_monitoring.sql;
-- hangs (preparing takes about five minutes on my Linux server)
session #1
=========
SQL> set list on;
SQL> commit; select * from mon$attachments where
mon$attachment_id<>current_connection
CON> and mon$remote_protocol > is not null;
-- ALSO HANGS untill execution plan will appear in session #2!
So, we can not querying MON$ATTACHMENTS during five minutes. And any other
MON$-tables too.
PS. Script "also_complex_but_NOT_trouble_in_preparing.sql" does not leads to
such trouble though it also too comples and also have lot of "calls" inside
itself.
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