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Posted to commits@druid.apache.org by "jtuglu1 (via GitHub)" <gi...@apache.org> on 2026/02/04 02:40:59 UTC
Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
jtuglu1 commented on code in PR #18966:
URL: https://github.com/apache/druid/pull/18966#discussion_r2761898386
##########
sql/src/main/java/org/apache/druid/sql/calcite/schema/BrokerSegmentMetadataCache.java:
##########
@@ -358,10 +358,34 @@ private Map<String, PhysicalDatasourceMetadata> queryDataSourceInformation(Set<S
private void updateDSMetadata(String dataSource, PhysicalDatasourceMetadata physicalDatasourceMetadata)
{
final PhysicalDatasourceMetadata oldTable = tables.put(dataSource, physicalDatasourceMetadata);
- if (oldTable == null || !oldTable.getRowSignature().equals(physicalDatasourceMetadata.getRowSignature())) {
- log.info("[%s] has new signature: %s.", dataSource, physicalDatasourceMetadata.getRowSignature());
+ final RowSignature newRowSignature = physicalDatasourceMetadata.getRowSignature();
+ final int newColumnCount = newRowSignature.getColumnNames().size();
+
+ final ServiceMetricEvent.Builder builder =
+ new ServiceMetricEvent.Builder().setDimension(DruidMetrics.DATASOURCE, dataSource);
+
+ if (oldTable == null) {
+ log.info(
+ "Row signature for datasource[%s] initialized with [%d] columns - signature[%s]",
+ dataSource, newColumnCount, newRowSignature
+ );
+
+ emitMetric(Metric.SCHEMA_ROW_SIGNATURE_INITIALIZED, 1, builder);
Review Comment:
Do we really need this `SCHEMA_ROW_SIGNATURE_INITIALIZED` metric? I wonder if it suffices to just look at the earliest `SCHEMA_ROW_SIGNATURE_COLUMN_COUNT` for a given deployment?
##########
docs/operations/metrics.md:
##########
@@ -462,6 +462,9 @@ These metrics are emitted by the Druid Coordinator in every run of the correspon
|`segment/schemaCache/dataSource/removed`|Emitted when a datasource is removed from the Broker cache due to segments being marked as unused.|`dataSource`||
|`segment/schemaCache/refresh/time`|Time taken to refresh segments in coordinator segment schema cache.|`dataSource`||
|`segment/schemaCache/backfill/count`|Number of segments for which schema was back filled in the database.|`dataSource`||
+|`segment/schemaCache/rowSignature/initialized`|Emitted when a datasource row signature is initialized for the first time in the Broker's segment metadata cache.|`dataSource`||
+|`segment/schemaCache/rowSignature/changed`|Emitted when the cached row signature on the Broker's segment metadata cache for a datasource changes, indicating schema evolution or some form of flapping.|`dataSource`||
+|`segment/schemaCache/rowSignature/column/count`|Number of columns in the updated row signature for a datasource.|`dataSource`||
Review Comment:
nit: `Number of columns in the row signature for a datasource.`
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