Thread: Why Index is not working on date columns.
Hi All,
Thank you very much for your help in configuring the database.
Can you guys please take a look at the following query and let me know why the index is not considered in the plan?
Here is the extract of the condition string of the query that is taking the transaction_date in index condition:
where (account.id = search_engine.account_fk) and ( account.status = 't' and account.id = '40288a820726362f0107263c55d00003') and ( search_engine.id = conversion.search_engine_fk and conversion.event_type ='daily_spend' and conversion.tactic = 'PPC' and conversion.transaction_date between '2005-01-01 00:00:00' and '2005-10-31 23:59:59') group by account.id;
Plan:
" -> Index Scan using conversion_all on "conversion" (cost=0.00..6.02 rows=1 width=98)"
" Index Cond: (((tactic)::text = 'PPC'::text) AND ((event_type)::text = 'daily_spend'::text) AND (transaction_date >= '2005-01-01 00:00:00'::timestamp without time zone) AND (transaction_date <= '2005-10-31 23:59:59'::timestamp without time zon (..)"
" Index Cond: (((tactic)::text = 'PPC'::text) AND ((event_type)::text = 'daily_spend'::text) AND (transaction_date >= '2005-01-01 00:00:00'::timestamp without time zone) AND (transaction_date <= '2005-10-31 23:59:59'::timestamp without time zon (..)"
Here is the extract of the condition string of the query that is not taking the transaction_date in index condition:
where ( account.status = 't' and account.id = search_engine.account_fk and account.id = '40288a820726362f0107263c55d00003' ) and ( search_engine.id = conversion.search_engine_fk and conversion.tactic = 'PPC' and conversion.transaction_date >= '2005-01-01 00:00:00' and conversion.transaction_date <= '2005-10-31 23:59:59' ) group by account.id ;
Plan:
" -> Index Scan using conv_evnt_tact_trans_date_sefk on "conversion" (cost=0.00..6.02 rows=1 width=132)"
" Index Cond: ((("outer".id)::text = ("conversion".search_engine_fk)::text) AND (("conversion".tactic)::text = 'PPC'::text))"
" Filter: ((transaction_date >= '2005-01-01 00:00:00'::timestamp without time zone) AND (transaction_date <= '2005-10-31 23:59:59'::timestamp without time zone))"
" Index Cond: ((("outer".id)::text = ("conversion".search_engine_fk)::text) AND (("conversion".tactic)::text = 'PPC'::text))"
" Filter: ((transaction_date >= '2005-01-01 00:00:00'::timestamp without time zone) AND (transaction_date <= '2005-10-31 23:59:59'::timestamp without time zone))"
I have the following indexes defined on the columns.
conv_evnt_tact_trans_date_sefk : (search_engine_fk, tactic, event_type, transaction_date);
conv_all : (tactic, event_type, transaction_date);
I am really confused when I saw this plan. In both queries, I am using the same columns in the where condition, but the optimizer is taking different indexes in these two cases.
Second, even though, I have the transaction_date column specified in the second instance, why is it not taking the constraint as index condition?
Thanks in advance.
Thank you,
Kishore.
Kishore B <kishorebh@gmail.com> writes:
> Can you guys please take a look at the following query and let me know why
> the index is not considered in the plan?
"Considered" and "used" are two different things.
The two examples you give have the same estimated cost (within two
decimal places) so the planner sees no particular reason to choose one
over the other.
I surmise that you are testing on toy tables and extrapolating to what
will happen on larger tables. This is an unjustified assumption.
Create a realistic test data set, ANALYZE it, and then see if the
planner chooses indexes you like.
regards, tom lane
Hi Tom,
Thank you for your response.
I surmise that you are testing on toy tables and extrapolating to what
will happen on larger tables.
These tables participating here contain more than 8 million records as of now, and on every day, 200K records, will add to them.
Thank you,
Kishore.
On 10/25/05, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Kishore B <kishorebh@gmail.com> writes:
> Can you guys please take a look at the following query and let me know why
> the index is not considered in the plan?
"Considered" and "used" are two different things.
The two examples you give have the same estimated cost (within two
decimal places) so the planner sees no particular reason to choose one
over the other.
I surmise that you are testing on toy tables and extrapolating to what
will happen on larger tables. This is an unjustified assumption.
Create a realistic test data set, ANALYZE it, and then see if the
planner chooses indexes you like.
regards, tom lane
Kishore B <kishorebh@gmail.com> writes:
>> I surmise that you are testing on toy tables and extrapolating to what
>> will happen on larger tables.
>>
> These tables participating here contain more than 8 million records as of
> now, and on every day, 200K records, will add to them.
In that case, have you ANALYZEd the tables lately? The planner's cost
estimates correspond to awfully small tables ...
regards, tom lane