Monitor SAI indexes
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SAI monitoring is not supported Astra DB. |
Use these tools to monitor secondary indexes that were created with Storage-Attached Indexing (SAI), including metrics and options for pre-configured dashboards.
CQL virtual tables
System virtual tables provide information about the status of SAI indexes.
The system_views.indexes provides information at the column index level.
This table includes the index name, number of indexed SSTables, disk usage, and the index state.
From the index state, the data reveals if the index is currently building, and whether the index can be queried.
When you DROP or recreate an SAI index, you are not blocked from entering queries that do not use the index.
However, you cannot use that SAI index (based on the same column) until it has finished building and is queryable.
To determine the current state of a given index, query the system_views.indexes virtual table.
Example:
SELECT is_queryable,is_building FROM system_views.indexes
WHERE keyspace_name='<keyspace>'
AND table_name='<table>'
AND index_name='<index>';The system_views.sstable_indexes describes individual SSTable indexes.
This table includes information about disk size, minimum and maximum row ID, the minimum and maximum ring token, and the write-time version of the index.
The system_views.sstable_index_segments describes the segments of the SSTable indexes.
This table exposes the segment row ID offset and most of the information in the SSTable-level virtual table, specifically at a segment granularity.
DataStax Enterprise tracing
DataStax Enterprise users can access enhanced tracing capability for SAI just like other DSE database components.
Information is captured by the system_traces keyspace.
You can enable tracing in CQLSH with TRACING ON, and you can enable request tracing in Cassandra drivers.
The number of rows filtered by a particular query will show up in the CQL query trace. Example:
Index query accessed memtable indexes, 2 SSTable indexes, and 2 segments, post-filtered 14 rows in 14 partitions, and took 88582 microseconds.For details about DSE tracing, refer to CQL TRACING.
SAI metrics
SAI provides a number of metrics to help you monitor the health of your indexes.
The metrics are categorized as:
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Global indexing metrics
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Table query metrics
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Per query metrics
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Key fetch metrics
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Offset fetch metrics
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Token fetch metrics
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Column query metrics per index
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Terms metrics per index
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Range slice metrics
For example, use metrics to get the current count of total partition reads since the node started for cycling.cyclist_semi_pro.
The keyspace and table were defined in SAI quickstart.
This metric’s ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=cycling,table=cyclist_semi_pro,scope=TableQueryMetrics,name=TotalPartitionReads.
The metrics are exposed via JMX, so any JMX-based tool can be used to monitor. Common tools include:
Global indexing metrics
ObjectName: org.apache.cassandra.metrics,type=StorageAttachedIndex,name=<metric>
The global indexing metrics for this node are:
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The number of individual on-disk column indexes currently being built. |
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The limit on heap used to buffer SSTable index segments during compaction and index builds. |
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The heap currently being used to buffer SSTable index segments during compaction and index builds. |
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At any given time, the minimum size for a flushing segment, in bytes, is ( |
Index group metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=IndexGroupMetrics,name=<metric>
The index group metrics for the given keyspace and table:
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Size in bytes on disk for the given table’s SAI indices. |
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Size in bytes of memory used by the on-disk data structure of the per-column indices. |
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Number of open index files for the given table’s SAI indices. |
Key fetch metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=KeyFetch,name=<metric>
The key fetch metrics for the given keyspace and table:
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All-time chunk cache hit rate for keys during queries against the given table. |
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All-time chunk cache lookups for keys during queries against the given table. |
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All-time chunk cache misses for keys during queries against the given table. |
`ChunkCache(One |
Five |
Fifteen)HitRate` |
<N>-minute chunk cache hit rate for keys during queries against the given table. |
Offset fetch metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=OffsetFetch,name=<metric>
The offset fetch metrics for the given keyspace and table:
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All-time chunk cache hit rate for partition key SSTable offset fetches during queries against the given table. |
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All-time chunk cache lookups for partition key SSTable offset fetches during queries against the given table. |
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All-time chunk cache misses for partition key SSTable offset fetches during queries against the given table. |
`ChunkCache(One |
Five |
Fifteen)HitRate` |
<N>-minute chunk cache hit rate for partition key SSTable offset fetches during queries against the given table. |
Per query metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=PerQuery,name=<metric>
The per query metrics for the given keyspace and table include:
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A histogram of the number of rows post-filtered per query since the node started. |
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Overall query latency percentiles (in microseconds) and one/five/fifteen minute query throughput. |
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Histogram over the number of partitions read per query. |
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Histogram over the number of SSTable indexes read per query. |
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Histogram over the number of chunk cache lookups while reading kd-tree index files per query. |
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Histogram over the number of chunk cache misses while reading kd-tree index files per query. |
Table query metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=TableQueryMetrics,name=<metric>
The table query metrics for the given keyspace and table:
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Total partition reads by all queries since the node started. |
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Total number of successfully completed queries since the node started. |
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Total number of timeouts from queries since the node started. |
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Total number of rows post-filtered by all queries since the node started. |
Table state metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=TableStateMetrics,name=<metric>
The table state metrics for the given keyspace and table:
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SAI size on Disk as a percentage of table size per table. |
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Size on-disk in bytes of SAI indices per table. |
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Status of SAI indices per table currently in the |
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Total number of SAI indices per table. |
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Status of SAI indices per table currently in the |
Token fetch metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=TokenFetch,name=<metric>
The token fetch metrics for the given keyspace and table:
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All-time chunk cache hit rate for partition key token fetches during queries against the given table. |
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All-time chunk cache lookups for partition key token fetches during queries against the given table. |
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All-time chunk cache misses for partition key token fetches during queries against the given table. |
`ChunkCache(One |
Five |
Fifteen)HitRate` |
<N>-minute chunk cache hit rate for partition key token fetches during queries against the given table. |
Token skipping metrics
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,scope=TokenSkipping,name=<metric>
The token skipping metrics for the given keyspace and table:
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Number of cache hits from token skipping in a multi-index |
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Number of lookups from token skipping a multi-index |
Column query metrics for each numeric index
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,index=<index>,scope=ColumnQueryMetrics,name=<metric>
The column query metrics for the given keyspace, table, and index include:
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For numeric indexes, such as |
Column query metrics for each string index
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,index=<index>,scope=ColumnQueryMetrics,name=<metric>
The column query metrics for the given keyspace, table, and index include:
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For string indexes, such as |
Terms metrics for each string index
ObjectName: org.apache.cassandra.metrics:type=StorageAttachedIndex,keyspace=<keyspace>,table=<table>,index=<index>,scope=Terms,name=<metric>
For string indexes, the terms metrics for the given keyspace, table, and index:
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All-time chunk cache hit rate for terms during string index queries that used the given index. |
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All-time chunk cache lookups for terms during string index queries that used the given index. |
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All-time chunk cache misses for terms during string index queries that used the given index. |
`ChunkCache(One |
Five |
Fifteen)HitRate` |
<N>-minute chunk cache hit rate for terms during string index queries that used the given index. |
Range slice metrics
ObjectName: org.apache.cassandra.metrics:type=ClientRequest,scope=RangeSlice,name=<metric>
The RoundTripsPerReadHistogram metric tracks the number of round-trip requests sent for range query commands from the coordinator.
Fewer requests typically mean the server is operating more efficiently than ones requiring more requests to satisfy the same range queries.
Latency metric tracks the min, max, mean as well as a set of percentiles for range read requests latency. Timeouts metric tracks the number of timeouts for range read requests.
