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Posted to commits@druid.apache.org by "abhishekrb19 (via GitHub)" <gi...@apache.org> on 2026/01/29 21:39:05 UTC
[PR] Add new metrics and logging for row signature flapping. (druid)
abhishekrb19 opened a new pull request, #18966:
URL: https://github.com/apache/druid/pull/18966
We keep encountering different row signatures for the same datasource. We’ll need to root cause why the schema “flaps” periodically, but my current suspicion is that this originates on the ingestion path when data is sparse + complex<json> columns - when this happens the columns in the row signature gets reordered.
The side effect of this row signature flapping is that SQL queries can be planned into incorrect native queries until the broker’s schema cache eventually reconciles back to the “correct” signature. This leads to sporadic missing data. Will include more details about the flapping behavior later.
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "jtuglu1 (via GitHub)" <gi...@apache.org>.
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 (since it's emitted in both cases).
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "jtuglu1 (via GitHub)" <gi...@apache.org>.
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 (since it's emitted in both cases). For "one-off" events I tend to lean towards logging them (and then for repeated events use metrics), although I suppose this would catch bugs where the table schema was getting cleared somehow. I'm not sure how much value adding the initialized metric provides given you would be checking logs anyways most likely to see old column count, etc.
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "jtuglu1 (via GitHub)" <gi...@apache.org>.
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 (since it's emitted in both cases). For "one-off" events I tend to lean towards logging them (and then for repeated events use metrics), although I suppose this would catch bugs where the table schema was getting cleared somehow.
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "abhishekrb19 (via GitHub)" <gi...@apache.org>.
abhishekrb19 commented on code in PR #18966:
URL: https://github.com/apache/druid/pull/18966#discussion_r2762640428
##########
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:
Right, I mainly added the `SCHEMA_ROW_SIGNATURE_INITIALIZED` metric to differentiate between the different code paths. I've removed it for now as you note the updated logs and the signature update metric should provide better insights.
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "abhishekrb19 (via GitHub)" <gi...@apache.org>.
abhishekrb19 commented on code in PR #18966:
URL: https://github.com/apache/druid/pull/18966#discussion_r2762640428
##########
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:
Right, I mainly added the `SCHEMA_ROW_SIGNATURE_INITIALIZED` metric to differentiate between the different code paths. I've removed it for now since the updated logs and the signature update &. column count metrics should provide better insights as you note.
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "jtuglu1 (via GitHub)" <gi...@apache.org>.
jtuglu1 commented on code in PR #18966:
URL: https://github.com/apache/druid/pull/18966#discussion_r2761889526
##########
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 initial/updated row signature for a datasource.`
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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "jtuglu1 (via GitHub)" <gi...@apache.org>.
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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Re: [PR] Add metrics and improve logging for row signature flapping. (druid)
Posted by "abhishekrb19 (via GitHub)" <gi...@apache.org>.
abhishekrb19 merged PR #18966:
URL: https://github.com/apache/druid/pull/18966
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