Quanlong Huang created IMPALA-13818:
---------------------------------------
Summary: Wasting space due to duplidated TColumnType between
THdfsPartitions
Key: IMPALA-13818
URL: https://issues.apache.org/jira/browse/IMPALA-13818
Project: IMPALA
Issue Type: Bug
Components: Backend, Frontend
Reporter: Quanlong Huang
Assignee: Quanlong Huang
Attachments: TDescriptorTable.png, THdfsPartition_mem_footprint-1.png
THdfsPartition is used in at least two places:
* In the legacy catalog mode, catalogd propagates metadata to coordinators.
* In TQueryExecRequest, it's used in the tableDescriptors sent to the backend
as part of query plans and fragments.
It has a list of expressions to represent the partition values:
{code:java}
struct THdfsPartition {
// These are Literal expressions
7: list<Exprs.TExpr> partitionKeyExprs
...
}{code}
E.g. here is a partition (year=2009, month=1) of the functional.alltypes table:
{noformat}
THdfsPartition {
07: partitionKeyExprs (list) = list<struct>[2] {
[0] = TExpr {
01: nodes (list) = list<struct>[1] {
[0] = TExprNode {
01: node_type (i32) = 2,
02: type (struct) = TColumnType {
01: types (list) = list<struct>[1] {
[0] = TTypeNode {
01: type (i32) = 0,
02: scalar_type (struct) = TScalarType {
01: type (i32) = 5,
},
},
},
},
03: num_children (i32) = 0,
04: is_constant (bool) = true,
11: int_literal (struct) = TIntLiteral {
01: value (i64) = 2009,
},
23: is_codegen_disabled (bool) = false,
},
},
},
[1] = TExpr {
01: nodes (list) = list<struct>[1] {
[0] = TExprNode {
01: node_type (i32) = 2,
02: type (struct) = TColumnType {
01: types (list) = list<struct>[1] {
[0] = TTypeNode {
01: type (i32) = 0,
02: scalar_type (struct) = TScalarType {
01: type (i32) = 5,
},
},
},
},
03: num_children (i32) = 0,
04: is_constant (bool) = true,
11: int_literal (struct) = TIntLiteral {
01: value (i64) = 1,
},
23: is_codegen_disabled (bool) = false,
},
},
},
},
09: file_desc (list) = list<struct>[1] {
[0] = THdfsFileDesc {
01: file_desc_data (string) =
"\x18\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0e\x00
\x00\x1c\x00\x10\x00\x00\x00\b\x00\x04\x00\x0e\x00\x00\x00\x1c\x00\x00\x00\xce\x80\x17\xf3\x93\x01\x00\x00\xd1O\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\f\x00\x00\x00\x01\x00\x00\x00
\x00\x00\x00\n\x00\x00\x00090101.txt\x00\x00\f\x00\x14\x00\x00\x00\f\x00\b\x00\x04\x00\f\x00\x00\x00\x10\x00\x00\x00\x18\x00\x00\x00\xd1O\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x01\x00\x02\x00\x00\x00\x03\x00\x00\x00\x02\x00\x01\x00\x00\x00\x00\x00",
},
},
10: location (struct) = THdfsPartitionLocation {
01: prefix_index (i32) = 0,
02: suffix (string) = "year=2009/month=1",
},
11: access_level (i32) = 1,
12: stats (struct) = TTableStats {
01: num_rows (i64) = 310,
},
13: is_marked_cached (bool) = false,
14: id (i64) = 1,
15: hms_parameters (map) = map<string,string>[8] {
"STATS_GENERATED" -> "TASK",
"impala.events.catalogServiceId" ->
"3378db64f1864d2a:afdb738fe029883c",
"impala.events.catalogVersion" -> "12277",
"numFiles" -> "1",
"numFilesErasureCoded" -> "0",
"numRows" -> "310",
"totalSize" -> "20433",
"transient_lastDdlTime" -> "1734950224",
},
16: num_blocks (i64) = 1,
17: total_file_size_bytes (i64) = 20433,
19: has_incremental_stats (bool) = false,
25: partition_name (string) = "year=2009/month=1",
26: prev_id (i64) = -1,
27: hdfs_storage_descriptor (struct) = THdfsStorageDescriptor {
01: lineDelim (byte) = 0x0a,
02: fieldDelim (byte) = 0x2c,
03: collectionDelim (byte) = 0x2c,
04: mapKeyDelim (byte) = 0x2c,
05: escapeChar (byte) = 0x5c,
06: quoteChar (byte) = 0x2c,
07: fileFormat (i32) = 0,
08: blockSize (i32) = 0,
},
}{noformat}
The partitionKeyExprs actually duplicates the partition column types, which is
a waste in memory or network transmission. Here is an example from a heap dump:
!THdfsPartition_mem_footprint.png|width=655,height=447!
The query reads a single table of 6M partitions and 6M files. It hits OOM of
exceeding the 2GB JVM byte array limit in serializing the DescriptorTable:
{noformat}
java.lang.Thread @ 0x7fdf6d220768 : Thread-12
at java.lang.OutOfMemoryError.<init>()V (OutOfMemoryError.java:48)
at java.util.Arrays.copyOf([BI)[B (Arrays.java:3236)
at java.io.ByteArrayOutputStream.toByteArray()[B
(ByteArrayOutputStream.java:191)
at org.apache.thrift.TSerializer.serialize(Lorg/apache/thrift/TBase;)[B
(TSerializer.java:85)
at
org.apache.impala.common.JniUtil.serializeToThrift(Lorg/apache/thrift/TBase;)[B
(JniUtil.java:109)
at
org.apache.impala.analysis.DescriptorTable.toSerializedThrift()Lorg/apache/impala/thrift/TDescriptorTableSerialized;
(DescriptorTable.java:260)
at
org.apache.impala.service.Frontend.getPlannedExecRequest(Lorg/apache/impala/service/Frontend$PlanCtx;Lorg/apache/impala/analysis/AnalysisContext$AnalysisResult;Lorg/apache/impala/util/EventSequence;)Lorg/apache/impala/thrift/TQueryExecRequest;
(Frontend.java:3138)
at
org.apache.impala.service.Frontend.doCreateExecRequest(Lorg/apache/impala/service/Frontend$PlanCtx;Ljava/util/List;Lorg/apache/impala/util/EventSequence;)Lorg/apache/impala/thrift/TExecRequest;
(Frontend.java:2893)
at
org.apache.impala.service.Frontend.getTExecRequest(Lorg/apache/impala/service/Frontend$PlanCtx;Lorg/apache/impala/util/EventSequence;)Lorg/apache/impala/thrift/TExecRequest;
(Frontend.java:2410)
at
org.apache.impala.service.Frontend.createExecRequest(Lorg/apache/impala/service/Frontend$PlanCtx;)Lorg/apache/impala/thrift/TExecRequest;
(Frontend.java:2036)
at org.apache.impala.service.JniFrontend.createExecRequest([B)[B
(JniFrontend.java:175){noformat}
The TDescriptorTable objects occupies 9.67GB memory. The duplicated partition
column types wasted arround 6.7GB (6M * 2 * 600 bytes) memory.
!TDescriptorTable.png|width=960,height=605!
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