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Posted to commits@cassandra.apache.org by "Caleb Rackliffe (Jira)" <ji...@apache.org> on 2020/11/12 17:06:00 UTC
[jira] [Commented] (CASSANDRA-16226) COMPACT STORAGE SSTables
created before 3.0 are not correctly skipped by timestamp due to missing
primary key liveness info
[ https://issues.apache.org/jira/browse/CASSANDRA-16226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17230788#comment-17230788 ]
Caleb Rackliffe commented on CASSANDRA-16226:
---------------------------------------------
With the now-committed CASSANDRA-16217 bringing back {{isCQLTable()}}, the patch currently posted for this issue is perhaps _more_ defensible. However, the problems around {{DROP COMPACT STORAGE}} persist and will have to be dealt with.
> COMPACT STORAGE SSTables created before 3.0 are not correctly skipped by timestamp due to missing primary key liveness info
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-16226
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16226
> Project: Cassandra
> Issue Type: Bug
> Components: Legacy/Local Write-Read Paths
> Reporter: Caleb Rackliffe
> Assignee: Caleb Rackliffe
> Priority: Normal
> Labels: perfomance, upgrade
> Fix For: 3.0.x, 3.11.x, 4.0-beta
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> This was discovered while tracking down a spike in the number of SSTables per read for a COMPACT STORAGE table after a 2.1 -> 3.0 upgrade. Before 3.0, there is no direct analog of 3.0's primary key liveness info. When we upgrade 2.1 COMPACT STORAGE SSTables to the mf format, we simply don't write row timestamps, even if the original mutations were INSERTs. On read, when we look at SSTables in order from newest to oldest max timestamp, we expect to have this primary key liveness information to determine whether we can skip older SSTables after finding completely populated rows.
> ex. I have three SSTables in a COMPACT STORAGE table with max timestamps 1000, 2000, and 3000. There are many rows in a particular partition, making filtering on the min and max clustering effectively a no-op. All data is inserted, and there are no partial updates. A fully specified row with timestamp 2500 exists in the SSTable with a max timestamp of 3000. With a proper row timestamp in hand, we can easily ignore the SSTables w/ max timestamps of 1000 and 2000. Without it, we read 3 SSTables instead of 1, which likely means a significant performance regression.
> The following test illustrates this difference in behavior between 2.1 and 3.0:
> https://github.com/maedhroz/cassandra/commit/84ce9242bedd735ca79d4f06007d127de6a82800
> A solution here might be as simple as having {{SinglePartitionReadCommand#canRemoveRow()}} only inspect primary key liveness information for non-compact/CQL tables. Tombstones seem to be handled at a level above that anyway. (One potential problem with that is whether or not the distinction will continue to exist in 4.0, and dropping compact storage from a table doesn't magically make pk liveness information appear.)
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