From: | yash mehta <yash215(at)gmail(dot)com> |
---|---|
To: | pgsql-performance(at)lists(dot)postgresql(dot)org |
Subject: | select distinct runs slow on pg 10.6 |
Date: | 2019-09-09 08:30:01 |
Message-ID: | CAMgY1WkxX43j47Na4GMHDsOrJQL4M30jw-_Q3qwAWGh8b-MAhQ@mail.gmail.com |
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Lists: | pgsql-performance |
We have a query that takes 1min to execute in postgres 10.6 and the same
executes in 4 sec in Oracle database. The query is doing 'select distinct'.
If I add a 'group by' clause, performance in postgres improves
significantly and fetches results in 2 sec (better than oracle). But
unfortunately, we cannot modify the query. Could you please suggest a way
to improve performance in Postgres without modifying the query.
*Original condition: time taken 1min*
Sort Method: external merge Disk: 90656kB
*After removing distinct from query: time taken 2sec*
Sort Method: top-N heapsort Memory: 201kB
*After increasing work_mem to 180MB; it takes 20sec*
Sort Method: quicksort Memory: 172409kB
SELECT * FROM pg_stat_statements ORDER BY total_time DESC limit 1;
-[ RECORD 1
]-------+-----------------------------------------------------------------------------------------------------------------------------------------
userid | 174862
dbid | 174861
queryid | 1469376470
query | <query is too long. It selects around 300 columns>
calls | 1
total_time | 59469.972661
min_time | 59469.972661
max_time | 59469.972661
mean_time | 59469.972661
stddev_time | 0
rows | 25
shared_blks_hit | 27436
shared_blks_read | 2542
shared_blks_dirtied | 0
shared_blks_written | 0
local_blks_hit | 0
local_blks_read | 0
local_blks_dirtied | 0
local_blks_written | 0
temp_blks_read | 257
temp_blks_written | 11333
blk_read_time | 0
blk_write_time | 0
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