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https://issues.apache.org/jira/browse/MADLIB-1224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16426367#comment-16426367
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Jingyi Mei commented on MADLIB-1224:
------------------------------------
For grouping, we propose to modify the current formula from
{code:java}
default_buffer_size = min(75000000.0/independent_var_dimension,
float(num_rows_processed)/num_of_segments){code}
To
{code:java}
default_buffer_size = min(75000000.0/independent_var_dimension,
float(avg_num_rows_processed_by_group)/num_of_segments){code}
Considerations are:
1. for 1GB per row limit, constraint `75000000.0/independent_var_dimension`
still works because `75000000.0/independent_var_dimension` won't change with
grouping
2. for data distribution, we want to data in each group gets distributed to all
segment, which means we have to use `min(num_rows_processed_per_group)` to do
the math, however, considering there might be extreme case that data is heavily
skewed to one group and there is other group which only get few records(like
1), the default_buffer_size will be 1 which basically does not pack data at
all, we propose to use the average number of rows processed by group to make a
balance.
> Select default buffer size for mini-batch preprocessor
> ------------------------------------------------------
>
> Key: MADLIB-1224
> URL: https://issues.apache.org/jira/browse/MADLIB-1224
> Project: Apache MADlib
> Issue Type: Improvement
> Components: Module: Utilities
> Reporter: Jingyi Mei
> Priority: Major
> Fix For: v1.14
>
>
> As a follow up of https://issues.apache.org/jira/browse/MADLIB-1200
>
> In minibatch_preprocessor, we made buffer_size as an optional parameter. If
> it is not set, some default value will be assigned. Current considerations
> are:
> # Within segment, each cell has 1GB limit so that we can't put too many rows
> into one super row to exceed the limit
> # Among segments, data should be distributed as equally as possible to avoid
> data skew so that GPDB can work more efficiently.
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