Insert operation at Azure SQL Synapse Analytics is running longer

Question

Hi,

We have DW500C system and observing strange behavior, which i would like to understand bit better.

we have a Fact load Insert statement that runs for more than an Hour and its direct execution of SELECT statement is completing within 15 minutes.

I have some doubt in terms of back end execution that showed at sys.dm_pdw_request_steps.

While this insert query is running and if i parallely verify the sys.dm_pdw_request_steps. I see the execution step jumps directly to step_index 27 as soon as i submit the query.

while it was in step_index 27 and long running there, i went to previous step_index and started checking the row_count column, all steps have rowcount as -1.

While it was in step_index=27, the Operation_type=OnOperation, Distribution_type=AllDistributions, Location_Type=Compute. and it remains in this step till the insert query completes.

This makes me weird in two ways, 1st thing is, execution step directly jumped to 27th step and if i track previous steps, rowcount all shows -1

Could you please help me to understand the output of sys.dm_pdw_request_steps? how the query works at the back end when i submit the INSERT statement.

That would give me some idea about execution plan.

Run time for the insert query is same for ROUND ROBIN and also with individual hash column and a set of HASH Columns distribution.

while testing this long running INSERT statement, nothing was running in parallel.

Performance is the same even if run the query under XLARGERC or STATICRC40.