Re: Regrading brin_index on required column of the table - Mailing list pgsql-general

The results of explain analyze would shed light on the core problem.

My guess is that your conditions are not very selective - ie. most
records in both tables have bFetch = false - and therefore you are
retrieving most of your data and that is what's taking 7 minutes. No
index is going to fix that.

If those boolean values are distributed very unevenly (say 99.9% has
false and 0.1% has true), you may get better results by excluding the
records with 'true' values (instead of including those that are
'false'), for example by using a where not exists(...) subquery.

Obviously, that still won't help if you're just fetching a lot of data.
On Wed, 19 Sep 2018 at 16:23, Durgamahesh Manne
<maheshpostgres9@gmail.com> wrote:
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> On Wed, Sep 19, 2018 at 7:41 PM Igor Neyman <ineyman@perceptron.com> wrote:
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>> From: Durgamahesh Manne [mailto:maheshpostgres9@gmail.com]
>> Sent: Wednesday, September 19, 2018 10:04 AM
>> To: Igor Neyman <ineyman@perceptron.com>
>> Subject: Re: Regrading brin_index on required column of the table
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>> On Wed, Sep 19, 2018 at 7:19 PM Igor Neyman <ineyman@perceptron.com> wrote:
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>> From: Durgamahesh Manne [mailto:maheshpostgres9@gmail.com]
>> Sent: Wednesday, September 19, 2018 9:43 AM
>> To: PostgreSQL mailing lists <pgsql-general@postgresql.org>
>> Subject: Regrading brin_index on required column of the table
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>> Hi
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>> Respected postgres community members
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>> I have created BRIN index on few columns of the table without any issues. But i am unable to create BRIN index on
onecolumn of the table as i got error listed below 
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>> [local]:6263 postgres@huawei=# CREATE INDEX brin_idx on huawei using brin ("dFetch");
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>> ERROR:  data type boolean has no default operator class for access method "brin"
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>> HINT:  You must specify an operator class for the index or define a default operator class for the data type.
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>>  below is the column description:
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>> Column     datatype   collation    nullable       default    storage
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>>  dFetch        boolean                                         false        plain
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>> so please help in creating of the BRIN index on above column of the table .
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>> Regards
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>> Durgamahesh Manne
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>> Why would you want BRIN index on Boolean-type column?
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>> What kind of interval will you specify?
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>> Regards,
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>> Igor Neyman
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>>  Hi
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>>  I have complex query like for ex  select  distinct sub_head."vchSubmittersCode" ,rec."vchFileName" ,
rec."vchCusipFundIDSubFundID", rec."vchFundUnitPrice"  ,  sub_head."vchValuationDate" ,rec."vchAdvisorLabel" from
"table1"rec join  "table2" sub_head on rec."vchSubmittersCode"=sub_head."vchSubmittersCode" where  rec."bFetch"=false
andsub_head."bFetch"=false ; 
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>> Query taken around 7 minutes time to execute without indexes on required columns
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>>  SO  i need to execute this distinct query at less time by creating indexes on required columns of the tables
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>> i have created brin indexes on vchsubmitterscode of two tables
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>> i am not able to create brin indexes on bfetch tables as i got a error  ERROR:  data type boolean has no default
operatorclass for access method "brin" 
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>> HINT:  You must specify an operator class for the index or define a default operator class for the data type.
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>> so please help in creating of the BRIN index on above column of the table as i need to reduce the query execution
time
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>> Regards
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>> Durgamahesh Manne
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>> Again, BRIN indexes are not design to work on Boolean columns. If you want to index Boolean column, just create
regularBTREE index. 
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>> Regards,
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>> Igor
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>  Hi
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> I have already tried with BTREE indexes & HASH indexes on required columns .but distinct query execution time was not
reduced
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> Query taken around 7 minutes time to execute with BTREE indexes & HASH indexes on required columns
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> Regards
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> Durgamahesh Manne
>


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