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https://issues.apache.org/jira/browse/CASSANDRA-20132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17916399#comment-17916399
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Dmitry Konstantinov edited comment on CASSANDRA-20132 at 1/23/25 1:06 PM:
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Honestly, I do not want to fight for it to be included into 5.0.x :)
I have implemented it in my fork for 4.1.x and 5.0.x to cover my needs, so I
would just suggest it for trunk only (as I got from the ML discussion the
majority prefers stability to getting such operational or performance
improvements in a near future).
I can prepare a new MR using trunk as a baseline.
was (Author: dnk):
Honestly, I do not want to fight for it to be included into 5.0.x :)
I have implemented it in my fork for 4.1.x and 5.0.x to cover my needs, so I
would just suggest it for trunk only (as I got from the ML discussion the
majority is prefer stability to getting such operational or performance
improvements in a near future).
I can prepare a new MR using trunk as a baseline.
> 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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