Tim Armstrong created IMPALA-7749:
-------------------------------------
Summary: Merge aggregation node memory estimate is incorrectly
influenced by limit
Key: IMPALA-7749
URL: https://issues.apache.org/jira/browse/IMPALA-7749
Project: IMPALA
Issue Type: Sub-task
Components: Frontend
Affects Versions: Impala 2.12.0, Impala 3.0, Impala 2.11.0, Impala 3.1.0
Reporter: Tim Armstrong
Assignee: Bikramjeet Vig
In the below query the estimate for node ID 3 is too low. If you remove the
limit it is correct.
{noformat}
[localhost:21000] default> set explain_level=2; explain select l_orderkey,
l_partkey, l_linenumber, count(*) from tpch.lineitem group by 1, 2, 3 limit 5;
EXPLAIN_LEVEL set to 2
Query: explain select l_orderkey, l_partkey, l_linenumber, count(*) from
tpch.lineitem group by 1, 2, 3 limit 5
+-------------------------------------------------------------------------------------------+
| Explain String
|
+-------------------------------------------------------------------------------------------+
| Max Per-Host Resource Reservation: Memory=43.94MB Threads=4
|
| Per-Host Resource Estimates: Memory=450MB
|
|
|
| F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
|
| | Per-Host Resources: mem-estimate=0B mem-reservation=0B
thread-reservation=1 |
| PLAN-ROOT SINK
|
| | mem-estimate=0B mem-reservation=0B thread-reservation=0
|
| |
|
| 04:EXCHANGE [UNPARTITIONED]
|
| | limit: 5
|
| | mem-estimate=0B mem-reservation=0B thread-reservation=0
|
| | tuple-ids=1 row-size=28B cardinality=5
|
| | in pipelines: 03(GETNEXT)
|
| |
|
| F01:PLAN FRAGMENT [HASH(l_orderkey,l_partkey,l_linenumber)] hosts=3
instances=3 |
| Per-Host Resources: mem-estimate=10.00MB mem-reservation=1.94MB
thread-reservation=1 |
| 03:AGGREGATE [FINALIZE]
|
| | output: count:merge(*)
|
| | group by: l_orderkey, l_partkey, l_linenumber
|
| | limit: 5
|
| | mem-estimate=10.00MB mem-reservation=1.94MB spill-buffer=64.00KB
thread-reservation=0 |
| | tuple-ids=1 row-size=28B cardinality=5
|
| | in pipelines: 03(GETNEXT), 00(OPEN)
|
| |
|
| 02:EXCHANGE [HASH(l_orderkey,l_partkey,l_linenumber)]
|
| | mem-estimate=0B mem-reservation=0B thread-reservation=0
|
| | tuple-ids=1 row-size=28B cardinality=6001215
|
| | in pipelines: 00(GETNEXT)
|
| |
|
| F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
|
| Per-Host Resources: mem-estimate=440.27MB mem-reservation=42.00MB
thread-reservation=2 |
| 01:AGGREGATE [STREAMING]
|
| | output: count(*)
|
| | group by: l_orderkey, l_partkey, l_linenumber
|
| | mem-estimate=176.27MB mem-reservation=34.00MB spill-buffer=2.00MB
thread-reservation=0 |
| | tuple-ids=1 row-size=28B cardinality=6001215
|
| | in pipelines: 00(GETNEXT)
|
| |
|
| 00:SCAN HDFS [tpch.lineitem, RANDOM]
|
| partitions=1/1 files=1 size=718.94MB
|
| stored statistics:
|
| table: rows=6001215 size=718.94MB
|
| columns: all
|
| extrapolated-rows=disabled max-scan-range-rows=1068457
|
| mem-estimate=264.00MB mem-reservation=8.00MB thread-reservation=1
|
| tuple-ids=0 row-size=20B cardinality=6001215
|
| in pipelines: 00(GETNEXT)
|
+-------------------------------------------------------------------------------------------+
{noformat}
The bug is that we use cardinality_ to cap the number of distinct values, but
cardinality_ is capped at the output limit.
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