why function taking table parameter runs so slow?

[Anonymous]

Hi,

fake Codes likely:

let
     table1 = sometableInSameQuery,
     table2 = anotherTableInSameQuery,
     #"Added Conditional Column" = Table.AddColumn(table2, "new column", each if [C1] = null then table1{[C1=[C2]]}[C3] else [C1])
in
    #"Added Conditional Column"

table2 has 5000+ rows, table1 has 800+ rows, content of table1 is gotten from JIRA REST API.

when apply changes, I found both table1 and table2 can be loaded very quick.  But the new query loaded very very slow. Why? I am wondering if table as function parameter consuming resource too much? Or does JIRA REST querying need every time when Table.AddColumn executed row by row?

[v-piga-msft]

Hi @Anonymous ,

Normally the performance may be caused by many factors. I'm afraid that your issue may caused by refering other queries.

You could refer to this similar thread firstly.

In addition, I'm not good at the performance for power query, hope @ImkeF could give further advice for your scenario.

Best Regards,

Cherry

[Anonymous]

hi,

@v-piga-msft, thanks for help!

After some google for instance , https://powerpivotpro.com/2017/07/power-query-refresh-speeds-suck, I firmed my guess about Power Query poor perfermance. 

And inspired by https://community.powerbi.com/t5/Desktop/Transformations-in-Power-Query-Very-Slow-Performance/td-p/5... Using DAX in lieu of Power Qurey M solved the pain.

But I still can not sure where power query perform so poorly, I suspect power query go to do JIRA request row by row. 

Regards