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https://issues.apache.org/jira/browse/PIG-1492?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thejas M Nair updated PIG-1492:
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Attachment: PIG-1492.1.patch
This patch updates the memory size calculations . This changes were made so
that the estimated sizes are closer to what is seen in 32 bit Java HotSpot(TM)
Server VM (build 10.0-b19, mixed mode).
It is based on some of the observations in
http://www.javamex.com/tutorials/memory/string_memory_usage.shtm . The header
sizes of objects has been taken to be 8 bytes. The objects size is rounded to
multiple of 8 bytes. Some other adjustments for minimum size of array in a
ArrayList were made based on observed size values.
The follow tables shows the tuple estimated sizes before/after the patch and
what is actually observed, for the types whose calculation logic changed -
|| type || num of columns of this type in the tuple || before || patched ||
observed ||
| BYTEARRAY with 5 bytes| 10|254 | 504|495 |
| BYTEARRAY with 5 bytes| 1000| 21044| 44064|44127 |
| DOUBLE| 10|364 | 264|255 |
| DOUBLE| 1000|32044 | 20064| 20127 |
| LONG |10 | 284|264 |255 |
| LONG | 1000 | 24044 | 20064 | 20127 |
|| Tuple containing a single - || patched || observed ||
| BAG with 10 empty tuples|524| 1092|1159 |
| BAG with 1000 empty tuples| 48044| 100092| 100211|
| map with 10 integer key-value pairs| 380| 824| 775|
| map with 1000 integer key-value pairs| 32060| 64184| 64346|
> DefaultTuple and DefaultMemory understimate their memory footprint
> ------------------------------------------------------------------
>
> Key: PIG-1492
> URL: https://issues.apache.org/jira/browse/PIG-1492
> Project: Pig
> Issue Type: Bug
> Reporter: Thejas M Nair
> Assignee: Thejas M Nair
> Fix For: 0.8.0
>
> Attachments: PIG-1492.1.patch
>
>
> There are several places where we highly underestimate the memory footprint .
> For example, for map datatypes, we don't account for the per entry cost for
> the map container data structures. The estimated size of a tuple having map
> with 100 integer key-value entries , as per current version of code is 3260
> bytes, while what is observed is around 6775 bytes . To verify the memory
> footprint, i checked free memory before and after creating multiple instances
> of the object , using code on the lines of
> http://www.javaspecialists.eu/archive/Issue029.html .
> In PIG-1443 similar change was done to fix this for CHARARRAY .
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