[
https://issues.apache.org/jira/browse/PIG-1295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12897958#action_12897958
]
Thejas M Nair commented on PIG-1295:
------------------------------------
bq. Conceptually comparator is in the logic of Tuple.
This comparator is part of only the *default* tuple implementation used
internally within pig. So the class that is the source of truth for the default
internal tuple implementation seems a good place to have this function. A tuple
returned by a loadfunction has nothing to do with the comparator logic.
bq. Ideally it should be a static method of Tuple, however Tuple interface do
not allow me do that.
Yes, a static method can't be overridden. Since this is supposed to return only
one value per pig query, the singleton TupleFactory is a better place.
bq. For backward compatibility, first, we will break either Tuple or
TupleFactory, the impact is equivalent;
No. TupleFactory is an abstract class, while Tuple is an interface. Users will
not be forced to change their implementation if we add a function to
TupleFactory. Also, users are more likely to have custom Tuple than custom
TupleFactory - because they might implement different tuples as part of their
load function implementation, and are unlikely to change the default Tuple
implementation used in internally in pig.
bq. second, in both PigSecondaryKeyComparator and PigTupleSortComparator, we
will check if Tuple does not implement the new method, we fall back to the
default serialize version.
If Tuple interface is going to have this function, i think we should add in the
javadoc that it makes sense to implement the function only if it is going to be
used as the default internal tuple implementation. And that
null value can be returned if user chooses to not implement it.
> Binary comparator for secondary sort
> ------------------------------------
>
> Key: PIG-1295
> URL: https://issues.apache.org/jira/browse/PIG-1295
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Affects Versions: 0.7.0
> Reporter: Daniel Dai
> Assignee: Gianmarco De Francisci Morales
> Fix For: 0.8.0
>
> Attachments: PIG-1295_0.1.patch, PIG-1295_0.10.patch,
> PIG-1295_0.11.patch, PIG-1295_0.12.patch, PIG-1295_0.13.patch,
> PIG-1295_0.14.patch, PIG-1295_0.2.patch, PIG-1295_0.3.patch,
> PIG-1295_0.4.patch, PIG-1295_0.5.patch, PIG-1295_0.6.patch,
> PIG-1295_0.7.patch, PIG-1295_0.8.patch, PIG-1295_0.9.patch
>
>
> When hadoop framework doing the sorting, it will try to use binary version of
> comparator if available. The benefit of binary comparator is we do not need
> to instantiate the object before we compare. We see a ~30% speedup after we
> switch to binary comparator. Currently, Pig use binary comparator in
> following case:
> 1. When semantics of order doesn't matter. For example, in distinct, we need
> to do a sort in order to filter out duplicate values; however, we do not care
> how comparator sort keys. Groupby also share this character. In this case, we
> rely on hadoop's default binary comparator
> 2. Semantics of order matter, but the key is of simple type. In this case, we
> have implementation for simple types, such as integer, long, float,
> chararray, databytearray, string
> However, if the key is a tuple and the sort semantics matters, we do not have
> a binary comparator implementation. This especially matters when we switch to
> use secondary sort. In secondary sort, we convert the inner sort of nested
> foreach into the secondary key and rely on hadoop to sorting on both main key
> and secondary key. The sorting key will become a two items tuple. Since the
> secondary key the sorting key of the nested foreach, so the sorting semantics
> matters. It turns out we do not have binary comparator once we use secondary
> sort, and we see a significant slow down.
> Binary comparator for tuple should be doable once we understand the binary
> structure of the serialized tuple. We can focus on most common use cases
> first, which is "group by" followed by a nested sort. In this case, we will
> use secondary sort. Semantics of the first key does not matter but semantics
> of secondary key matters. We need to identify the boundary of main key and
> secondary key in the binary tuple buffer without instantiate tuple itself.
> Then if the first key equals, we use a binary comparator to compare secondary
> key. Secondary key can also be a complex data type, but for the first step,
> we focus on simple secondary key, which is the most common use case.
> We mark this issue to be a candidate project for "Google summer of code 2010"
> program.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
