What does stats partitions do?

[ryhluc01]

What does stats partitions do? How would you use this?

Sample query:

|stats **partitions=1** latest(Insert_Text) by field_1 field_2 

The partition and by fields can be whatever you specify. I just would like to understand what is going on here.

[lstewart_splunk]

The partitions argument runs the reduce step (in parallel reduce processing) with multiple threads in the same search process on the same machine. Compare that with parallel reduce that runs the reduce step in parallel on multiple machines.

Parallel reduce is implemented with the redistribute command: https://docs.splunk.com/Documentation/Splunk/latest/SearchReference/Redistribute

In testing, the run times for a search using partitions=5 shows no difference as compared to partitions=1, using this search:

| makeresults count=5000000
| streamstats count as i
| eval a=floor(i/10), b=floor(i/100), c=floor(i/1000), d=floor(i/10000), e=floor(i/100000)
| stats partitions=5 count by a, b, c, d, e

In this example, we are able to observe an ~9 second difference in run times:

| makeresults count=500000
| streamstats count as i
| eval j=mvrange(0,10)
| stats partitions=15 count by i,j

With partitions=15 the search completes in 27 seconds. With partitions=1 the search completes in 36 seconds.

The likely issue with the partitions argument as compared to the redistribute command, is the threads are competing for memory on the same machine - and memory usage is one of the significant factors that cause high-cardinality stats to perform poorly. Partitioning the memory usage across different machines, as the redistribute command does, eliminates that competition.

[woodcock]

Well the dox say that 1 is the default value for partitions so your search can drop it with no change. The documentation is useless on this parameter. You ask a good question.

[ryhluc01]

Right? The documentation on the subject is not helpful at all. Thanks @woodcock. Now I am just hoping someone else will know.

[woodcock]

I submitted feedback at the bottom of the documentation page, asking for more detail.

[ryhluc01]

Thanks @woodcock! You're the best.

[woodcock]

If everybody in any community does his little part, the experience for everybody improves dramatically.