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https://issues.apache.org/jira/browse/PIG-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Clément Stenac updated PIG-3310:
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Attachment: generate-uid-for-nested-fields.patch
> ImplicitSplitInserter does not generate new uids for nested schema fields,
> leading to miscomputations
> -----------------------------------------------------------------------------------------------------
>
> Key: PIG-3310
> URL: https://issues.apache.org/jira/browse/PIG-3310
> Project: Pig
> Issue Type: Bug
> Components: impl
> Affects Versions: 0.11.1
> Environment: Reproduced on 0.10.1, 0.11.1 and trunk
> Reporter: Clément Stenac
> Attachments: generate-uid-for-nested-fields.patch
>
>
> Hi,
> Consider the following example
> {code}
> inp = LOAD '$INPUT' AS (memberId:long, shopId:long, score:int);
> tuplified = FOREACH inp GENERATE (memberId, shopId) AS tuplify, score;
> D1 = FOREACH tuplified GENERATE tuplify.memberId as memberId, tuplify.shopId
> as shopId, score AS score;
> D2 = FOREACH tuplified GENERATE tuplify.memberId as memberId, tuplify.shopId
> as shopId, score AS score;
> J = JOIN D1 By shopId, D2 by shopId;
> K = FOREACH J GENERATE D1::memberId AS member_id1, D2::memberId AS
> member_id2, D1::shopId as shop;
> EXPLAIN K;
> DUMP K;
> {code}
> It is a bit weird written like that, but it provides a minimal reproduction
> case (in the real case, the "tuplified" phase came from a multi-key grouping).
> On input data:
> {code}
> 1 1001 101
> 1 1002 103
> 1 1003 102
> 1 1004 102
> 2 1005 101
> 2 1003 101
> 2 1002 123
> 3 1042 101
> 3 1005 101
> 3 1002 133
> {code}
> This will give a wrongful output like ..
> {code}
> (1,1001,1001)
> (1,1002,1002)
> (1,1002,1002)
> (1,1002,1002)
> {code}
> The second column should be a member id so (1,2,3,4,5).
> In the initial case, there was a FILTER (member_id1 < member_id2) after K,
> and computation failed because of PushUpFilter optimization mistakenly moving
> the LOFilter operation before the join, at a place where it tried to work on
> a tuple and failed.
> My understanding of the issue is that when the ImplicitSplitInserter creates
> the LOSplitOutputs, it will correctly reset the schema, and the LOSplitOutput
> will regenerate uids for the fields of D1 and D2 ... but will not do that on
> the tuple members.
> The logical plan after the ImplicitSplitINserter will look like (simplified)
> {code}
> |---D1: (Name: LOForEach Schema:
> memberId#124:long,shopId#125:long)ColumnPrune:InputUids=[127]ColumnPrune:OutputUids=[125,
> 124]
> |---tuplified: (Name: LOSplitOutput Schema:
> tuplify#127:tuple(memberId#124:long,shopId#125:long))ColumnPrune:InputUids=[123]ColumnPrune:OutputUids=[127]
> |---tuplified: (Name: LOSplit Schema:
> tuplify#123:tuple(memberId#124:long,shopId#125:long))ColumnPrune:InputUids=[123]ColumnPrune:OutputUids=[123]
> |---D2: (Name: LOForEach Schema:
> memberId#124:long,shopId#125:long)ColumnPrune:InputUids=[130]ColumnPrune:OutputUids=[125,
> 124]
> |---tuplified: (Name: LOSplitOutput Schema:
> tuplify#130:tuple(memberId#124:long,shopId#125:long))ColumnPrune:InputUids=[123]ColumnPrune:OutputUids=[130]
> |---tuplified: (Name: LOSplit Schema:
> tuplify#123:tuple(memberId#124:long,shopId#125:long))ColumnPrune:InputUids=[123]ColumnPrune:OutputUids=[123]
> {code}
> tuplified correctly gets a new uid (127 and 130) but the members of the tuple
> don't. When they get reprojected, both branches have the same uid and the
> join looks like:
> {code}
> |---J: (Name: LOJoin(HASH) Schema:
> D1::memberId#124:long,D1::shopId#125:long,D2::memberId#139:long,D2::shopId#132:long)ColumnPrune:InputUids=[125,
> 124, 132]ColumnPrune:OutputUids=[125, 124, 132]
> | |
> | shopId:(Name: Project Type: long Uid: 125 Input: 0 Column: 1)
> | |
> | shopId:(Name: Project Type: long Uid: 125 Input: 1 Column: 1)
> {code}
> If for example instead of reprojecting "memberId", we project "memberId+0", a
> new node is created, and ultimately the two branches of the join will
> correctly get separate uids.
> My understanding is that LOSplitOutput.getSchema() should recurse on nested
> schema fields. However, I only have a light understanding of all of the
> logical plan handling, so I may be completely wrong.
> Attached is a draft of patch and a test reproducing the issue. Unfortunately,
> I haven't been able to run all unit tests with the "fix" (I have some weird
> hangs)
> I'd be happy if you could indicate if that looks like completely the wrong
> way to fix the issue.
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