Re: Query puts 7.3.4 on endless loop but 7.4beta5 is fine. - Mailing list pgsql-performance

Hi ,

Here are the Execution Plans ,
Sorry for the delay .

Regds
Mallah

On PostgreSQL  7.3.4

rt3=# explain   SELECT DISTINCT main.* FROM ((((Tickets main  JOIN Groups as Groups_1  ON ( main.id = Groups_1.Instance))  
JOIN Principals as Principals_2  ON ( Groups_1.id = Principals_2.ObjectId)) JOIN CachedGroupMembers as CachedGroupMembers_3  
ON ( Principals_2.id = CachedGroupMembers_3.GroupId))  JOIN Users as Users_4  ON ( CachedGroupMembers_3.MemberId = Users_4.id))   
WHERE ((main.EffectiveId = main.id)) AND ((main.Type = 'ticket')) AND ( (  ( (Users_4.EmailAddress = 'mallah_rajesh@yahoo.com')
AND(Groups_1.Domain = 'RT::Ticket-Role')AND(Groups_1.Type = 'Requestor')AND(Principals_2.PrincipalType = 'Group') )  ) 
AND ( (main.Status = 'new')OR(main.Status = 'open') ) )  ORDER BY main.Priority DESC LIMIT 10;

Limit  (cost=2044.52..2044.58 rows=1 width=195)  ->  Unique  (cost=2044.52..2044.58 rows=1 width=195)        ->  Sort  (cost=2044.52..2044.52 rows=1 width=195)              Sort Key: main.priority, main.id, main.effectiveid, main.queue, main."type", main.issuestatement, main.resolution, main."owner", main.subject, main.initialpriority, main.finalpriority, main.timeestimated, main.timeworked, main.status, main.timeleft, main.told, main.starts, main.started, main.due, main.resolved, main.lastupdatedby, main.lastupdated, main.creator, main.created, main.disabled              ->  Hash Join  (cost=3.98..2044.51 rows=1 width=195)                    Hash Cond: ("outer".memberid = "inner".id)                    ->  Nested Loop  (cost=0.00..2040.51 rows=2 width=191)                          ->  Nested Loop  (cost=0.00..1914.41 rows=1 width=183)                                ->  Nested Loop  (cost=0.00..1909.67 rows=1 width=175)                                      Join Filter: (("outer".id)::text = ("inner".instance)::text)                                      ->  Seq Scan on tickets main  (cost=0.00..465.62 rows=1 width=163)                                            Filter: ((effectiveid = id) AND ("type" = 'ticket'::character varying) AND ((status = 'new'::character varying) OR (status = 'open'::character varying)))                                      ->  Index Scan using groups_domain on groups groups_1  (cost=0.00..1338.03 rows=7068 width=12)                                            Index Cond: ("domain" = 'RT::Ticket-Role'::character varying)                                            Filter: ("type" = 'Requestor'::character varying)                                ->  Index Scan using principals2 on principals principals_2  (cost=0.00..4.73 rows=1 width=8)                                      Index Cond: ("outer".id = principals_2.objectid)                                      Filter: (principaltype = 'Group'::character varying)                          ->  Index Scan using cachedgroupmembers3 on cachedgroupmembers cachedgroupmembers_3  (cost=0.00..125.54 rows=45 width=8)                                Index Cond: ("outer".id = cachedgroupmembers_3.groupid)                    ->  Hash  (cost=3.98..3.98 rows=1 width=4)                          ->  Index Scan using users4 on users users_4  (cost=0.00..3.98 rows=1 width=4)                                Index Cond: (emailaddress = 'mallah_rajesh@yahoo.com'::character varying)
(23 rows)

On PostgreSQL 7.4 beta 5

rt3=# explain   SELECT DISTINCT main.* FROM ((((Tickets main  JOIN Groups as Groups_1  ON ( main.id = Groups_1.Instance))  
JOIN Principals as Principals_2  ON ( Groups_1.id = Principals_2.ObjectId)) JOIN CachedGroupMembers as CachedGroupMembers_3  
ON ( Principals_2.id = CachedGroupMembers_3.GroupId))  JOIN Users as Users_4  ON ( CachedGroupMembers_3.MemberId = Users_4.id))   
WHERE ((main.EffectiveId = main.id)) AND ((main.Type = 'ticket')) AND ( (  ( (Users_4.EmailAddress = 'mallah_rajesh@yahoo.com')
AND(Groups_1.Domain = 'RT::Ticket-Role')AND(Groups_1.Type = 'Requestor')AND(Principals_2.PrincipalType = 'Group') )  ) 
AND ( (main.Status = 'new')OR(main.Status = 'open') ) )  ORDER BY main.Priority DESC LIMIT 10;                                                                                                                                                                                                      QUERY PLAN
---------------------------------------------------------------Limit  (cost=582.27..582.34 rows=1 width=164)  ->  Unique  (cost=582.27..582.34 rows=1 width=164)        ->  Sort  (cost=582.27..582.28 rows=1 width=164)              Sort Key: main.priority, main.id, main.effectiveid, main.queue, main."type", main.issuestatement, main.resolution, main."owner", main.subject, main.initialpriority, main.finalpriority, main.timeestimated, main.timeworked, main.status, main.timeleft, main.told, main.starts, main.started, main.due, main.resolved, main.lastupdatedby, main.lastupdated, main.creator, main.created, main.disabled              ->  Hash Join  (cost=476.18..582.26 rows=1 width=164)                    Hash Cond: ("outer".groupid = "inner".id)                    ->  Nested Loop  (cost=0.00..105.97 rows=21 width=4)                          ->  Index Scan using users4 on users users_4  (cost=0.00..3.99 rows=2 width=4)                                Index Cond: ((emailaddress)::text = 'mallah_rajesh@yahoo.com'::text)                          ->  Index Scan using cachedgroupmembers2 on cachedgroupmembers cachedgroupmembers_3  (cost=0.00..50.81 rows=14 width=8)                                Index Cond: (cachedgroupmembers_3.memberid = "outer".id)                    ->  Hash  (cost=476.17..476.17 rows=1 width=168)                          ->  Nested Loop  (cost=0.00..476.17 rows=1 width=168)                                ->  Nested Loop  (cost=0.00..471.54 rows=1 width=168)                                      ->  Seq Scan on tickets main  (cost=0.00..465.62 rows=1 width=164)                                            Filter: ((effectiveid = id) AND (("type")::text = 'ticket'::text) AND (((status)::text = 'new'::text) OR ((status)::text = 'open'::text)))                                      ->  Index Scan using groups1 on groups groups_1  (cost=0.00..5.90 rows=1 width=12)                                            Index Cond: (((groups_1."domain")::text = 'RT::Ticket-Role'::text) AND (("outer".id)::text = (groups_1.instance)::text) AND ((groups_1."type")::text = 'Requestor'::text))                                ->  Index Scan using principals2 on principals principals_2  (cost=0.00..4.62 rows=1 width=8)                                      Index Cond: ("outer".id = principals_2.objectid)                                      Filter: ((principaltype)::text = 'Group'::text)
(21 rows)

rt3=#

Christopher Browne wrote:

In the last exciting episode, mallah@trade-india.com wrote: 

mallah@trade-india.com (Rajesh Kumar Mallah) wrote:     

Can you please have a Look at the below and suggest why it
apparently puts 7.3.4 on an infinite loop . the CPU utilisation of the backend running it
approches 99%.       

What would be useful, for this case, would be to provide the query plan, perhaps via
EXPLAIN [Big Long Query].

The difference between that EXPLAIN and what you get on 7.4 might be quite interesting.

I would think it quite unlikely that it is truly an "infinite" loop; it is rather more likely
that the plan winds up being pretty bad and doing something [a bunch of nested loops, maybe?]
that run longer than your patience will permit.     

:-)   ok i will leave it running and try to get it.   

No, if you just do EXPLAIN (and not EXPLAIN ANALYZE), that returns
without executing the query.

If the query runs for a really long time, then we _know_ that there is
something troublesome.  EXPLAIN (no ANALYZE) should provide some
insight without having anything run for a long time.

If EXPLAIN [big long query] turns into what you are terming an
"infinite loop," then you have a quite different problem, and it would
be very useful to know that.