Re: How allowDiskUse is executed

From: Markus Thielsch <markus.thielsch@xxxxxxxxxxx>
To: mongodb-user <mongodb-user@xxxxxxxxxxxxxxxx>
Date: Thu, 28 Apr 2016 23:14:12 -0700 (PDT)
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Hi Przemysław,

When the [`allowDiskUse` 
parameter](https://docs.mongodb.org/manual/reference/command/aggregate/#aggregate-data-using-external-sort
is set to `true` MongoDB will only start using the local disk once the RAM 
limit is exceeded.

For more general information on limitations have a look at the [Memory 
Restrictions 
documentation](https://docs.mongodb.org/manual/core/aggregation-pipeline-limits/#memory-restrictions).

Regards,
Markus


On Friday, April 29, 2016 at 12:29:22 AM UTC+10, Rhys Campbell wrote:

https://docs.mongodb.org/manual/reference/command/aggregate/

"Optional. Enables writing to temporary files. When set to true, 
aggregation stages can write data to the _tmp subdirectory in the dbPath 
<https://docs.mongodb.org/manual/reference/configuration-options/#storage.dbPath>
 directory."

Says can here so that's must mean only if it needs to. Related note take a 
look at this optimization...


https://docs.mongodb.org/manual/core/aggregation-pipeline-optimization/#sort-limit-coalescence


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