From: | jian xu <jamesxu(at)outlook(dot)com> |
---|---|
To: | "pgsql-admin(at)postgresql(dot)org" <pgsql-admin(at)postgresql(dot)org> |
Subject: | how to calibrate the cost model parameters |
Date: | 2022-05-29 15:29:55 |
Message-ID: | BL0PR02MB45619FD7E496D38966D33E5CA1DA9@BL0PR02MB4561.namprd02.prod.outlook.com |
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Lists: | pgsql-admin |
Hello,
On my system, the estimated query cost has huge difference with the real query cost. For example, a simple select query, the estimated query cost is 100X bigger than real cost, I think I need to calibrate the cost model parameters below(I still use default value)
#seq_page_cost = 1.0 # measured on an arbitrary scale
#random_page_cost = 4.0 # same scale as above
#cpu_tuple_cost = 0.01 # same scale as above
#cpu_index_tuple_cost = 0.005 # same scale as above
#cpu_operator_cost = 0.0025 # same scale as above
I googled it, and only find some suggestions, for example set random_page_cost to 1 or 2 for SSD, however, there is no doc about how to calibrate the cost model parameters to make the estimated query cost close to the real query cost.
Thanks,
James
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