What is spark.driver.maxResultSize?

Question

The ref says:

Limit of total size of serialized results of all partitions for each Spark action (e.g. collect). Should be at least 1M, or 0 for unlimited. Jobs will be aborted if the total size is above this limit. Having a high limit may cause out-of-memory errors in driver (depends on spark.driver.memory and memory overhead of objects in JVM). Setting a proper limit can protect the driver from out-of-memory errors.

What does this attribute do exactly? I mean at first (since I am not battling with a job that fails due to out of memory errors) I thought I should increase that.

On second thought, it seems that this attribute defines the max size of the result a worker can send to the driver, so leaving it at the default (1G) would be the best approach to protect the driver..

But will happen on this case, the worker will have to send more messages, so the overhead will be just that the job will be slower?

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If I understand correctly, assuming that a worker wants to send 4G of data to the driver, then having spark.driver.maxResultSize=1G, will cause the worker to send 4 messages (instead of 1 with unlimited spark.driver.maxResultSize). If so, then increasing that attribute to protect my driver from being assassinated from Yarn should be wrong.

But still the question above remains..I mean what if I set it to 1M (the minimum), will it be the most protective approach?

Lorylose

Answer 1

assuming that a worker wants to send 4G of data to the driver, then having spark.driver.maxResultSize=1G, will cause the worker to send 4 messages (instead of 1 with unlimited spark.driver.maxResultSize).

No. If estimated size of the data is larger than maxResultSize given job will be aborted. The goal here is to protect your application from driver loss, nothing more.

if I set it to 1M (the minimum), will it be the most protective approach?

In sense yes, but obviously it is not useful in practice. Good value should allow application to proceed normally but protect application from unexpected conditions.

Increscent

Setting it to 0 for unlimited is highly convenient right up until that makes things crash. – Gettings

Why setting maxResultSize to max is not a good option? How does it make driver fail? – Mosora

because Driver do lot of things! (care of workers, block manager etc...) no heap enough => crash. – Jame

So, if you set it to a low value.... it' crashes too! It's kinda like an assert(): you hit a condition you don't want and either it'll stop because of the assert or it'll crash because it hit a heap limit. If you don't do the assert in theory it'll take more before the heap crash (possibly with disk thrashing while swapping). – Andris

@ThomasDecaux What does the maxResultSize have to do with the driver memory heap? Does setting maxResultSize too high cause the result sizes to grow more than normally? – Willdon

Whether increasing the limit makes sense depends on how much memory the driver actually has. These days, the default of 1GB of memory free (on top of other responsibilities of the driver, like query plan storage etc.) doesn't seem like that much, so probably increasing the default at least is usually a good idea. – Mcdavid