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Reading execution plan - first row time vs last row time

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Dear community,

 

We see significant difference in explain analyze Actual time in the first line of execution plan and Execution time in the last line of execution plan. What can be the reason?

 

For example, first line of execution plan:

Gather  (cost=1038.49..257627100.42 rows=7943222226 width=104) (actual time=531.925..3673159.806 rows=7943221053 loops=1)

 

This is 3673159/1000/60 = 61 minutes

 

And last 2 lines of execution plan:

Planning Time: 3000.399 ms

Execution Time: 21208130.602 ms

 

This is : 21208130/1000/60= 353 minutes

 

 

What happened in 353 – 61 = 292 minutes? We speculate that disk writes. Query possibly written cca 0,75TB of data, by create table as select query.

 


S pozdravem

Ján Pecsők

Tychonova 2, 160 00 Praha
Mobil: +420 775 942 871
jan.pecsok@xxxxxxxxxxx
www.profinit.eu

 


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