Visualized Plan

I want to compare a query plan with and without reflections and I am not sure what the 3 Projection in a row mean.
I thought for threading or for Fragments but without reflections Dremio shows in the jobs only 1 thread and 1 fragment and with reflections it shows 3 threads and 3 fragments.

Another question is: you don’t need a UnionExchange operator in the plan without reflections because there is only one fragment and you don’t have to merge, right?

I am confused. I hope you can help me.

I am running this query on a single node cluster:

SELECT YaleLanguages_3.“MFHD_ID”, YaleLanguages_2.“Calculation_1810108111146429”, YaleLanguages_3. “Calculation_3110108110633423” FROM “@dremio”.YaleLanguages_3 INNER JOIN “@dremio”.YaleLanguages_2 on YaleLanguages_3.“MFHD_ID” = YaleLanguages_2.“MFHD_ID” WHERE ((YaleLanguages_2.“CHARGE_DATE” >= cast(‘2002-01-01’ as DATE)) AND (YaleLanguages_2.“PATRON_TYPE (Pseudo vs Patron)” = ‘Patron’)); (18,7 KB) (20,7 KB) (264,0 KB) (277,9 KB)


Job ID “20222a42-05d3-7b39-07d9-d0b32a508100” which is not accelerated is single threaded as both scans are reading only one file, See planning tab-final physical transformation and see the Easyscan and in both you will see “splits=[1]”, parallelism depends on number of rows, splits and cores in the box, but will be limited even if one of them is too low. PROJECT means Dremio is doing some kind of transformation, I can see “CONVERT_TO_INTEGER” and some Calculations

As far as the profile that is accelerated, only the phases are more but all phases are single threaded as we are only reading one split still

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ah okay I understand every Phase is single threaded but the execution of a phase is threaded.

but I have another question:
why does the accelerated plan have three colors?
should the colors represent different levels of planning? If so, which stages would these be?



Each phase is shown under a different color. Since the accelerated query has 3 phases, it has 3 colors, since the other profile has a single phase, it shows only one color