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https://issues.apache.org/jira/browse/CASSANDRA-20132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17916390#comment-17916390
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Stefan Miklosovic commented on CASSANDRA-20132:
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Also, is 5.0.x really what we want? So 5.0.x and trunk? Two branches? Based on
the recent discussion on ML it would be appropriate to ask if this is indeed
going to 5.0 as well. This is an improvement, not a bug fix. Improvements go to
trunk only (most of the time).
> 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: cpu_profile_select_cell.html, profile.yaml,
> trace_sample.txt
>
> Time Spent: 2h 10m
> 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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