[
https://issues.apache.org/jira/browse/CASSANDRA-21321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18084333#comment-18084333
]
Dmitry Konstantinov commented on CASSANDRA-21321:
-------------------------------------------------
yes, in case of batches we may have multiple rows as a part of PartitionUpdate
and the cost of this operation can be quite different, so it makes sense to
count number of rows additionally to the number of operations
> Add RowsRead and RowsMutated counters to TableMetrics for accurate per-table
> row throughput tracking
> ----------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21321
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21321
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Observability/Metrics
> Reporter: Piotr Walczak
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 7.x
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> Cassandra already exposes {{LiveScannedHistogram}} (rows returned per read)
> and {{RowsMutatedPerWriteHistogram}} (rows touched per write -
> https://issues.apache.org/jira/browse/CASSANDRA-21320) at the table level.
> These histograms are valuable for understanding the *distribution* of rows
> per operation, but they are *insufficient for measuring total row throughput*
> over a time window — which is essential for capacity planning and predictions.
> Specifically:
> * A histogram records _how many rows a single operation touched_ (e.g.,
> "this query returned 47 rows").
> * To derive total rows from a histogram you would need to multiply bucket
> midpoints by counts — an approximation that becomes increasingly inaccurate
> for skewed distributions.
> * Histograms also do not give you a simple delta between two scrape
> timestamps, making windowed rate calculations fragile.
> A *monotonically-increasing counter* solves all of these problems: scrape the
> value at {{t1}} and {{{}t2{}}}, subtract, divide by the interval — exact
> rows/sec with no approximation.
>
> Changes can look similar to:
> [https://github.com/apache/cassandra/compare/trunk...pwalczak:cassandra:pwalczak/CASSANDRA-21321?expand=1]
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
