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https://issues.apache.org/jira/browse/CASSANDRA-16226?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Caleb Rackliffe updated CASSANDRA-16226:
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Test and Documentation Plan:
The patch includes a series of new tests in {{SSTablesIteratedTest}} that
verify expected numbers of SSTables read for several query types across compact
and non-compact tables. They should serve as reasonable documentation and
guardrails against further regression.
The official [docs on compact
storage|https://cassandra.apache.org/doc/latest/cql/appendices.html#appendix-c-dropping-compact-storage]
and the in-tree docs (in {{ddl.rst}})will need some rework as well, both to
indicate that it will live on in 4.0, and to take into account the concerns in
this issue.
was:
The patch includes a series of new tests in {{SSTablesIteratedTest}} that
verify expected numbers of SSTables read for several query types across compact
and non-compact tables. They should serve as reasonable documentation and
guardrails against further regression.
The official [docs on compact
storage|https://cassandra.apache.org/doc/latest/cql/appendices.html#appendix-c-dropping-compact-storage]
will need some rework as well, both to indicate that it will live on in 4.0,
and to take into account the concerns in this issue.
> 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: 2h
> 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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