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Date: Thu, 14 Sep 2017 01:33:00 +0000 (UTC)
From: "Matthew Hayes (JIRA)" <jira@apache.org>
To: dev@datafu.incubator.apache.org
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Subject: [jira] [Commented] (DATAFU-119) New UDF - TupleDiff
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archived-at: Thu, 14 Sep 2017 01:33:05 -0000


    [ https://issues.apache.org/jira/browse/DATAFU-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16165598#comment-16165598 ] 

Matthew Hayes commented on DATAFU-119:
--------------------------------------

Also it would be useful to have a page in the guide that demonstrated the usage of TupleDiff and the macro.  We can do this separately.

> New UDF - TupleDiff
> -------------------
>
>                 Key: DATAFU-119
>                 URL: https://issues.apache.org/jira/browse/DATAFU-119
>             Project: DataFu
>          Issue Type: New Feature
>            Reporter: Eyal Allweil
>            Assignee: Eyal Allweil
>
> A UDF that given two tuples, prints out the differences between them in human-readable form. This is not meant for production - we use it in PayPal for regression tests, to compare the results of two runs. Differences are calculated based on position, but the tuples' schemas are used, if available, for displaying more friendly results. If no schema is available the output uses field numbers.
> It should be used when you want a more fine-grained description of what has changed, unlike [org.apache.pig.builtin.DIFF|https://pig.apache.org/docs/r0.14.0/func.html#diff]. Also, because DIFF takes as its input two bags to be compared, they must fit in memory. This UDF only takes one pair of tuples at a time, so it can run on large inputs.
> We use a macro much like the following in conjunction with this UDF:
> {noformat}
> DEFINE diff_macro(diff_macro_old, diff_macro_new, diff_macro_pk, diff_macro_ignored_field) returns diffs {
> 	DEFINE TupleDiff datafu.pig.util.TupleDiff;
> 		
> 	old = 	FOREACH $diff_macro_old GENERATE $diff_macro_pk, TOTUPLE(*) AS original;
> 	new = 	FOREACH $diff_macro_new GENERATE $diff_macro_pk, TOTUPLE(*) AS original;
> 	
> 	join_data = JOIN new BY $diff_macro_pk full, old BY $diff_macro_pk;
> 		
> 	join_data = FOREACH join_data GENERATE TupleDiff(old::original, new::original, '$diff_macro_ignored_field') AS tupleDiff, old::original, new::original;
> 		
> 	$diffs = FILTER join_data BY tupleDiff IS NOT NULL ;
> };
> {noformat}
> Currently, the output from the macro looks like this (when comma-separated):
> {noformat}
> added,<original tuple>,
> missing,,<new tuple>
> changed field2 field4,<original tuple>,<new tuple>
> {noformat}
> The UDF takes a variable number of parameters - the two tuples to be compared, and any number of field names or numbers to be ignored. We use this to ignore fields representing execution or creation time (the macro I've given as an example assumes only one ignored field)
> The current implementation "drills down" into tuples, but not bags or maps - tuple boundaries are indicated with parentheses, like this:
> {noformat}
> changed outerEmbeddedTuple(innerEmbeddedTuple(fieldNameThatIsDifferent) innerEmbeddedTuple(anotherFieldThatIsDifferent))
> {noformat}
> I have a few final things left to do and then I'll put it up on reviewboard.


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