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Add maximum shard size to config #4986

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merged 1 commit into from Jun 29, 2021
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Add maximum shard size to config #4986

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9 changes: 9 additions & 0 deletions distributed/distributed-schema.yaml
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Expand Up @@ -629,6 +629,15 @@ properties:
This is useful if you want to include serialization in profiling data,
or if you have data types that are particularly sensitive to deserialization

shard:
type: string
description: |
The maximum size of a frame to send through a comm

Some network infrastructure doesn't like sending through very large messages.
Dask comms will cut up these large messages into many small ones.
This attribute determines the maximum size of such a shard.

socket-backlog:
type: integer
description: |
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1 change: 1 addition & 0 deletions distributed/distributed.yaml
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Expand Up @@ -165,6 +165,7 @@ distributed:
min: 1s # the first non-zero delay between re-tries
max: 20s # the maximum delay between re-tries
compression: auto
shard: 64MiB
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nitpick but the previous value was 64MB not 64MiB :)

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Fair point. I think that we should default to powers of two in general. Any objection?

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@fjetter fjetter Jun 29, 2021 •
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I think that we should default to powers of two in genera

I guess it doesn't really matter but with powers of two we probably have the best chance to hit some kind of sweet mem alignment/cache size/whatever optimization so I'm all for it.

However, if you prefer powers of two, you should use MB, shoudn't you? (I understand if you didn't want to push changes any more, just wondering if I messed something up in my mind :) )

MB == 1024 ** 2 / 2 ** 20
MiB == 1000 ** 2 / 10**6

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From the internet, the source of all truth.

Megabytes (MB) or Mebibytes (MiB)?

Though the article refers to Linux, the topic is applicable to all computers. ... According to these standards, technically a megabyte (MB) is a power of ten, while a mebibyte (MiB) is a power of two, appropriate for binary machines. A megabyte is then 1,000,000 bytes.Dec 23, 2001

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wow, I was wrong all those years. I remember a first semester class where my prof introduced the unit and I would've sworn all these years it was the other way round 🤦

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Maybe the prof was wrong too? Imagine how they feel :)

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If he was wrong, he'd never admit to it!

offload: 10MiB # Size after which we choose to offload serialization to another thread
default-scheme: tcp
socket-backlog: 2048
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4 changes: 3 additions & 1 deletion distributed/protocol/utils.py
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@@ -1,8 +1,10 @@
import struct

import dask

from ..utils import nbytes

BIG_BYTES_SHARD_SIZE = 2 ** 26
BIG_BYTES_SHARD_SIZE = dask.utils.parse_bytes(dask.config.get("distributed.comm.shard"))


msgpack_opts = {
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