[
https://issues.apache.org/jira/browse/AVRO-1428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13872676#comment-13872676
]
Tie Liu commented on AVRO-1428:
-------------------------------
To explain the problem more clearly, in current implementation, when computing
the hashcode for the RecordSchema:
@Override
int computeHash()
{
...
return super.computeHash() + fields.hashCode();
}
the fields.hashCode will go through the fields and compute the hashCode for
that schema of the field.
Now when computing the hashcode for another recordSchema, it's doing the same
thing, compute the hashCode for the fields of the new schema gain, though maybe
the schema of the fields has already been computed before. The patch I propose
is to avoid recalculate the hashcode if we already calculated them before.
> Schema.computeHash() to add if check to avoid unnecessary hashcode computation
> ------------------------------------------------------------------------------
>
> Key: AVRO-1428
> URL: https://issues.apache.org/jira/browse/AVRO-1428
> Project: Avro
> Issue Type: Improvement
> Components: java
> Reporter: Tie Liu
> Attachments: AVRO-1428.patch, AVRO-1428.patch-V2, TestAvro.java
>
>
> In current Schma.java we have following implementation:
> public final int hashCode() {
> if (hashCode == NO_HASHCODE)
> hashCode = computeHash();
> return hashCode;
> }
> int computeHash() { return getType().hashCode() + props.hashCode(); }
> While hashCode is doing the checking of "if (hashCode == NO_HASHCODE)", the
> computeHash method is not. But the computeHash method is being called from
> Schema$Field.hashCode and the subclasses hashCode implementation like
> following:
> public int hashCode() { return name.hashCode() + schema.computeHash(); }
> //this is from Schema$Field class
> This is causing the the calculation of hashCode getting called
> unnecessarily extensively. The proposed changed is to add the "if" check
> inside the computeHash method instead:
> int computeHash()
> {
> if (hashCode == NO_HASHCODE)
> {
> hashCode = getType().hashCode() + props.hashCode();
> }
> return hashCode;
> }
> We did a simple test to compare the performance difference, below is a
> summary of the heap snapshot of comparing the difference:
> As a test I wrote a small program that creates a HashMap<Schema.Field,
> Integer>() and enters a loop simply identifying whether various Schema.Field
> instances are keys in the map. Obviously this is a pathological test case,
> but when running with the current implementation of Schema.Field it has (in
> about 30 seconds) used up nearly 8 GBytes of heap in instantiating
> intermediate objects associated with calling Schema.computeHash():
> Heap
> PSYoungGen total 17432576K, used 8666481K [0x0000000340000000,
> 0x0000000800000000, 0x0000000800000000)
> eden space 14942208K, 58% used
> [0x0000000340000000,0x0000000550f5c650,0x00000006d0000000)
> from space 2490368K, 0% used
> [0x0000000768000000,0x0000000768000000,0x0000000800000000)
> to space 2490368K, 0% used
> [0x00000006d0000000,0x00000006d0000000,0x0000000768000000)
> ParOldGen total 1048576K, used 0K [0x0000000300000000,
> 0x0000000340000000, 0x0000000340000000)
> object space 1048576K, 0% used
> [0x0000000300000000,0x0000000300000000,0x0000000340000000)
> PSPermGen total 21504K, used 5782K [0x00000002fae00000,
> 0x00000002fc300000, 0x0000000300000000)
> object space 21504K, 26% used
> [0x00000002fae00000,0x00000002fb3a5818,0x00000002fc300000)
> When running with the modified implementation (and no other change) all the
> object allocation vanishes:
> Heap
> PSYoungGen total 17432576K, used 896532K [0x0000000340000000,
> 0x0000000800000000, 0x0000000800000000)
> eden space 14942208K, 6% used
> [0x0000000340000000,0x0000000376b852d0,0x00000006d0000000)
> from space 2490368K, 0% used
> [0x0000000768000000,0x0000000768000000,0x0000000800000000)
> to space 2490368K, 0% used
> [0x00000006d0000000,0x00000006d0000000,0x0000000768000000)
> ParOldGen total 1048576K, used 0K [0x0000000300000000,
> 0x0000000340000000, 0x0000000340000000)
> object space 1048576K, 0% used
> [0x0000000300000000,0x0000000300000000,0x0000000340000000)
> PSPermGen total 21504K, used 5768K [0x00000002fae00000,
> 0x00000002fc300000, 0x0000000300000000)
> object space 21504K, 26% used
> [0x00000002fae00000,0x00000002fb3a2240,0x00000002fc300000)
> As a side-effect the test runs x3 faster with the modified hashCode()
> implementation.
--
This message was sent by Atlassian JIRA
(v6.1.5#6160)
