# Interaction between peach and other optimisations

**URL:** <https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090>\
**Category:** Community Support\
**Tags:** kdb-and-q\
**Created:** [November 17, 2023, 2:35pm UTC](https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090 "2023-11-17T14:35:00Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![erichards1](https://avatars.discourse-cdn.com/v4/letter/e/7feea3/32.png) [@erichards1](https://forum.kx.com/u/erichards1)\
**Post date:** [November 17, 2023, 2:35pm UTC](https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090/1 "2023-11-17T14:35:00Z")

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I understand there are various parallel optimisations that happen under the hood when running with some number of secondary threads, e.g. summing across multiple partitions. How do these interact with peach?

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For example:

disk0/hdb/par.txt –\> disk1/hdb/partitions , disk2/hdb/partitions disk1/hdb/partitions/1-3-5 disk2/hdb/partitions/2-4-6

If I ran a query such as

select sum price by sym where int within (1;4)

and I had two secondary threads available, thread #1 would retrieve data from partitions 1, 3 on disk 1, and thread #2 would retrieve data from partitions 2, 4 on disk 2 to maximise I/O throughput.

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But if my queries were wrapped in peach, would this still be possible, given peach would be using all available threads, e.g.

{x} peach ( {select sum price by sym where int within (1;4)}; {select sum price by sym where int within (5;6)} )

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So are there situations when using peach can reduce performance? Thank you

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<div class="post-metadata">

**Author:** ![erichards1](https://avatars.discourse-cdn.com/v4/letter/e/7feea3/32.png) [@erichards1](https://forum.kx.com/u/erichards1)\
**Post date:** [November 17, 2023, 2:36pm UTC](https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090/2 "2023-11-17T14:36:00Z")

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I guess a more succint version of my question is “what happens to native parallelisations when running queries inside an instance of peach?”

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**Author:** ![rocuinneagain1](https://avatars.discourse-cdn.com/v4/letter/r/fbc32d/32.png) [@rocuinneagain1](https://forum.kx.com/u/rocuinneagain1)\
**Post date:** [November 17, 2023, 2:59pm UTC](https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090/3 "2023-11-17T14:59:00Z")

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The parallelism can only go one layer deep.

.i.ie These 2 statements end up executing the same path. In the first one the inner `peach`&nbsp; can only run like an `each` as it is already in a thread:&nbsp;

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data:8#enlist til 1000000 \ts {{neg x} peach x} peach data 553 1968 \ts {{neg x} each x} peach data 551 1936

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For queries map-reduce still will be used to reduce the memory load of your nested queries even if run inside a ``peach` even if not running the sub parts in parallel.

https://code.kx.com/q4m3/14\_Introduction\_to\_Kdb%2B/#1437-map-reduce&nbsp;

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Where you choose to put your `peach` can be important and change the performance of your execution.

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My example actually runs better without peach due to the overhead of passing data around versus `neg` being a simple operation

\ts {{neg x} each x} each data 348 91498576

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.Q.fc exists to help in these cases

\ts {.Q.fc[{neg x};x]} each data 19 67110432

https://code.kx.com/q/ref/dotq/#fc-parallel-on-cut&nbsp; &nbsp;

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And in fact since `neg` has native multithreading and operates on vectors and vectors of vectors it is best of off left on it’s own:&nbsp;

\ts neg each data 5 67109216 \ts neg data 5 67109104 neg data

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This example of course is extreme but does show that thought and optimisation can go in to each use-case on where to choose to iterate and place `peach``

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<div class="post-metadata">

**Author:** ![erichards1](https://avatars.discourse-cdn.com/v4/letter/e/7feea3/32.png) [@erichards1](https://forum.kx.com/u/erichards1)\
**Post date:** [November 20, 2023, 11:34am UTC](https://forum.kx.com/t/interaction-between-peach-and-other-optimisations/13090/4 "2023-11-20T11:34:00Z")

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Many thanks for the reply and examples.

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> in fact since `neg` has native multithreading and operates on vectors and vectors of vectors it is best of off left on it’s own
> 
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This is what I was keen to understand, and it’s useful to know that there are cases when you may be better off without peach.