Abinayaa Tharmmarajhan created HBASE-30332:
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Summary: ProtobufUtil.toResult() silently discards QueryMetrics
for empty (row-not-found) results
Key: HBASE-30332
URL: https://issues.apache.org/jira/browse/HBASE-30332
Project: HBase
Issue Type: Bug
Components: Client, IPC/RPC
Reporter: Abinayaa Tharmmarajhan
When a {{Get}} is issued with {{setQueryMetricsEnabled(true)}} and the
requested row does not exist, the {{{}QueryMetrics{}}}(specifically
{{{}blockBytesScanned{}}}) are silently dropped during protobuf serialization.
The client always receives {{result.getMetrics() == null}} for missing rows,
even though the server did read blocks (bloom filters, index blocks) to
determine the row is absent and correctly computed the byte count.
*Steps to Reproduce*
# Issue a {{Get}} against a row that does not exist, with
{{get.setQueryMetricsEnabled(true)}}
# Check {{result.getMetrics()}} on the returned {{Result}}
# Observe {{null}} despite blocks having been read server-side
*Expected Behavior*
{{result.getMetrics().getBlockBytesScanned()}} returns the number of bytes read
to determine the row is absent — the same as it would for a row that exists.
*Root cause*
Based on some analysis, in {{ProtobufUtil.toResult(Result result, boolean
encodeTags)}} and {{{}ProtobufUtil.toResultNoData(Result result){}}}, when a
result has no cells, the code takes an early-return path that returns one of
six pre-built static proto constants. This could be causing the QueryMetrics to
be dropped for such cases.
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