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https://issues.apache.org/jira/browse/DATAFU-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15471164#comment-15471164
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Eyal Allweil commented on DATAFU-119:
-------------------------------------
Any feedback about this?
> 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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