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https://issues.apache.org/jira/browse/CASSANDRA-20132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17911577#comment-17911577
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Dmitry Konstantinov commented on CASSANDRA-20132:
-------------------------------------------------
[~clohfink] regarding
[https://github.com/apache/cassandra/pull/3730#discussion_r1901322433]
Thank you for noticing it. I have created PurgeableTombstonesMetricRecording
iterator based on the similar existing MetricRecording iterator logic. It looks
like the existing tombstoneScannedHistogram has the same behaviour. Should I
change considerZeroes = true for tombstoneScannedHistogram and add the counter
increment on a partition delete to MetricRecording as well?
> Add metric and tracing event for scanned purgeable tombstones
> -------------------------------------------------------------
>
> Key: CASSANDRA-20132
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20132
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Other
> Reporter: Dmitry Konstantinov
> Assignee: Dmitry Konstantinov
> Priority: Normal
> Fix For: 5.0.x
>
> Attachments: trace_sample.txt
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> Currently, Cassandra can read data from SSTables with tombstones and later
> drop them silently if the tombstones are older than gc_grace_seconds (aka
> purgeable tombstones). Such tombstones are not visible via
> readTombstoneHistogram metric, not reported in Cassandra logs if tombstone
> threshold is crossed and not mentioned in tracing events. As a result if a
> partition has a lot of purgeable tombstones we may have a slow read query
> without any signs why it is it slow. Example: [^trace_sample.txt]
> This suggested improvement adds:
> 1) a new metric which tracks number of such tombstones:
> PurgeableTombstoneScannedHistogram
> 2) a new tracing event: "Read {} purgeable tombstone cells" if number of such
> tombstones > 0
>
> Implementation notes: the logic of new withMetricsRecording iterator is an
> adjusted version of existing withMetricsRecording iterator
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