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From "Andy Seaborne (Commented) (JIRA)" <>
Subject [jira] [Commented] (JENA-97) TDB 0.9.0 snapshot sometimes returns a SELECT binding twice
Date Sat, 08 Oct 2011 15:26:30 GMT


Andy Seaborne commented on JENA-97:

Simon -

I presume you actually mean the same variable appears in the iterator of variables more than
once.  The bindings themselves (rows) have no duplicates.  The variable should not be repeated
but it is always bound to the same value.The var/value is cached in the immediate TDB level,
with it's NodeId, by copy-down from the parent. Only one is accessed by "get" and the variable
should only appear once in teh list of variable names.

In the results table above, there are no duplicates (some spellings are very similar).  Execution
proceeds by finding 3 choices for ?aUri. These pass to the path.  There are 3 possibilties
for ?aUri = <eomer.nt>, 2 for <eomer.nt> and 1 for <theodred.nt>.  TDB agrees
with an in-memory execution.

TDB 0.8.7 didn't always correctly execute paths outside the storage default graph so the query,
for other reasons, returned no rows.
> TDB 0.9.0 snapshot sometimes returns a SELECT binding twice
> -----------------------------------------------------------
>                 Key: JENA-97
>                 URL:
>             Project: Jena
>          Issue Type: Bug
>          Components: TDB
>         Environment: tx-tdb-0.9.0-20111006.082548-13-dist
>            Reporter: Simon Helsen
>            Assignee: Andy Seaborne
>         Attachments: quads.txt
> Very sometimes (rare), it seems that a result set will repeat the first SELECT binding.
> SELECT ?a ?b ...
> will bind ?a twice in the result set. It only happens quite rarely, but the same queries
behave correctly in TDB 0.8.7.

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