Eyal Allweil created DATAFU-119:
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Summary: 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:
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 ;
};
Currently, the output from the macro looks like this (when comma-separated):
added,<original tuple>,
missing,,<new tuple>
changed field2 field4,<original tuple>,<new tuple>
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:
changed outerEmbeddedTuple(innerEmbeddedTuple(fieldNameThatIsDifferent)
innerEmbeddedTuple(anotherFieldThatIsDifferent))
I have a few final things left to do and then I'll put it up on reviewboard.
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