RE: Simple Query Elapsed Time ~ 3 hrs Using Bitmap Index/Heap Scan

Indexes are being redone as per these insights. Appreciate the great support.

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Thank you

From: Matthew Hall
Sent: Tuesday, June 5, 2018 10:42 AM
To: Fred Habash
Cc: pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: Simple Query Elapsed Time ~ 3 hrs Using Bitmap Index/Heap Scan

Probably the cardinality of "vclf_number" is really bad. So the scan on that index is returning many million or billion rows and then you get a recheck which takes semi-forever. So you need an index on cl_value or both vclf_number and cl_value. If you know some properties of the values actually stored inside of those that will help. 
Matthew Hall

On Jun 5, 2018, at 7:17 AM, Fred Habash <fmhabash(at)gmail(dot)com> wrote:
Trying to optimize the Elapsed Time (ET) of this query. Currently, it is hovering around 3 hrs.
Running a 'vaccum analyse' had no effect on ET. Even forcing an 'indexonly' scan by disabling 'enable_seqscan', still around the 3 hrs.
The table is around 4.6B rows,
 explain select cit_id, cl_value from reflink.citation_locators where cl_value = '1507617681' and vclf_number = 1 ;
                                       QUERY PLAN                                       
-----------------------------------------------------------------------------------------
 Bitmap Heap Scan on citation_locators  (cost=5066559.01..50999084.79 rows=133 width=23)
   Recheck Cond: (vclf_number = 1)
   Filter: (cl_value = '1507617681'::text)
   ->  Bitmap Index Scan on cl_indx_fk02  (cost=0.00..5066558.97 rows=493984719 width=0)
         Index Cond: (vclf_number = 1)
(5 rows)
reflink.citation_locators
Table "reflink.citation_locators"
Column | Type | Modifiers | Storage | Stats target | Description
------------------+--------------------------+-----------+----------+--------------+-------------
cl_id | bigint | not null | plain | |
cl_value | text | not null | extended | |
vclf_number | integer | not null | plain | |
cit_id | bigint | not null | plain | |
cl_date_created | timestamp with time zone | not null | plain | |
cl_date_modified | timestamp with time zone | | plain | |
Indexes:
"cl_pk" PRIMARY KEY, btree (cl_id)
"cl_cnst_uk01" UNIQUE CONSTRAINT, btree (cit_id, vclf_number, cl_value)
"cl_indx_fk01" btree (cit_id)
"cl_indx_fk02" btree (vclf_number)
Foreign-key constraints:
"cl_cnst_fk01" FOREIGN KEY (cit_id) REFERENCES citations(cit_id) NOT VALID "cl_cnst_fk02" FOREIGN KEY (vclf_number) REFERENCES valid_cit_locator_fields(vclf_number)