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https://issues.apache.org/jira/browse/IMPALA-7360?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tim Armstrong resolved IMPALA-7360.
-----------------------------------
Resolution: Fixed
Fix Version/s: Impala 3.1.0
> Avro scanner sometimes skips blocks when skip marker is on HDFS block boundary
> ------------------------------------------------------------------------------
>
> Key: IMPALA-7360
> URL: https://issues.apache.org/jira/browse/IMPALA-7360
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 2.10.0, Impala 2.11.0, Impala 3.0, Impala 2.12.0
> Reporter: Tim Armstrong
> Assignee: Tim Armstrong
> Priority: Blocker
> Labels: avro, correctness
> Fix For: Impala 3.1.0
>
>
> The Avro changes in IMPALA-3905 introduced a correctness bug. You can hit it
> organically if you have a large avro file where the 16 byte sync marker
> straddles a block boundary. In that case the block after the sync marker may
> not be scanned, resulting in a few records missing.
> It's possible to reproduce on our test data by tweaking max_scan_range_length
> until you find a value where count(*) returns fewer results.
> {code}
> [localhost:21000] default> set max_scan_range_length=256k; select count(*)
> from tpch_avro_snap.lineitem;
> MAX_SCAN_RANGE_LENGTH set to 256k
> Query: select count(*) from tpch_avro_snap.lineitem
> Query submitted at: 2018-07-26 10:08:21 (Coordinator:
> http://tarmstrong-box:25000)
> Query progress can be monitored at:
> http://tarmstrong-box:25000/query_plan?query_id=5142ec7a702e67ac:b6882a6f00000000
> +----------+
> | count(*) |
> +----------+
> | 6001215 |
> +----------+
> Fetched 1 row(s) in 6.77s
> [localhost:21000] default> set max_scan_range_length=255k; select count(*)
> from tpch_avro_snap.lineitem;
> MAX_SCAN_RANGE_LENGTH set to 255k
> Query: select count(*) from tpch_avro_snap.lineitem
> Query submitted at: 2018-07-26 10:08:31 (Coordinator:
> http://tarmstrong-box:25000)
> Query progress can be monitored at:
> http://tarmstrong-box:25000/query_plan?query_id=3d40e63dacaac65b:99d17eaf00000000
> +----------+
> | count(*) |
> +----------+
> | 6000679 |
> +----------+
> Fetched 1 row(s) in 1.33s
> {code}
> We do have test coverage in TestScanRangeLengths that exercise the code with
> avro blocks straddling scan ranges. However, the necessary condition for this
> bug is that the scan range includes a full avro block, followed by a sync
> marker on the boundary with the next scan range. We need to add test coverage
> for a larger range of values here - larger files and larger scan ranges.
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