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Stefania commented on CASSANDRA-8180: ------------------------------------- Thanks for the review Branimir! The patch for trunk is [here|https://github.com/stef1927/cassandra/commits/8180], rebased and squashed. Launched one more CI round, if all good will move the ticket to ready to commit: ||trunk|| |[testall|http://cassci.datastax.com/view/Dev/view/stef1927/job/stef1927-8180-testall/]| |[dtest|http://cassci.datastax.com/view/Dev/view/stef1927/job/stef1927-8180-dtest/]| > Optimize disk seek using min/max column name meta data when the LIMIT clause > is used > ------------------------------------------------------------------------------------ > > Key: CASSANDRA-8180 > URL: https://issues.apache.org/jira/browse/CASSANDRA-8180 > Project: Cassandra > Issue Type: Improvement > Components: Local Write-Read Paths > Environment: Cassandra 2.0.10 > Reporter: DOAN DuyHai > Assignee: Stefania > Priority: Minor > Fix For: 3.x > > Attachments: 8180_001.yaml, 8180_002.yaml > > > I was working on an example of sensor data table (timeseries) and face a use > case where C* does not optimize read on disk. > {code} > cqlsh:test> CREATE TABLE test(id int, col int, val text, PRIMARY KEY(id,col)) > WITH CLUSTERING ORDER BY (col DESC); > cqlsh:test> INSERT INTO test(id, col , val ) VALUES ( 1, 10, '10'); > ... > >nodetool flush test test > ... > cqlsh:test> INSERT INTO test(id, col , val ) VALUES ( 1, 20, '20'); > ... > >nodetool flush test test > ... > cqlsh:test> INSERT INTO test(id, col , val ) VALUES ( 1, 30, '30'); > ... > >nodetool flush test test > {code} > After that, I activate request tracing: > {code} > cqlsh:test> SELECT * FROM test WHERE id=1 LIMIT 1; > activity | > timestamp | source | source_elapsed > ---------------------------------------------------------------------------+--------------+-----------+---------------- > execute_cql3_query | > 23:48:46,498 | 127.0.0.1 | 0 > Parsing SELECT * FROM test WHERE id=1 LIMIT 1; | > 23:48:46,498 | 127.0.0.1 | 74 > Preparing statement | > 23:48:46,499 | 127.0.0.1 | 253 > Executing single-partition query on test | > 23:48:46,499 | 127.0.0.1 | 930 > Acquiring sstable references | > 23:48:46,499 | 127.0.0.1 | 943 > Merging memtable tombstones | > 23:48:46,499 | 127.0.0.1 | 1032 > Key cache hit for sstable 3 | > 23:48:46,500 | 127.0.0.1 | 1160 > Seeking to partition beginning in data file | > 23:48:46,500 | 127.0.0.1 | 1173 > Key cache hit for sstable 2 | > 23:48:46,500 | 127.0.0.1 | 1889 > Seeking to partition beginning in data file | > 23:48:46,500 | 127.0.0.1 | 1901 > Key cache hit for sstable 1 | > 23:48:46,501 | 127.0.0.1 | 2373 > Seeking to partition beginning in data file | > 23:48:46,501 | 127.0.0.1 | 2384 > Skipped 0/3 non-slice-intersecting sstables, included 0 due to tombstones | > 23:48:46,501 | 127.0.0.1 | 2768 > Merging data from memtables and 3 sstables | > 23:48:46,501 | 127.0.0.1 | 2784 > Read 2 live and 0 tombstoned cells | > 23:48:46,501 | 127.0.0.1 | 2976 > Request complete | > 23:48:46,501 | 127.0.0.1 | 3551 > {code} > We can clearly see that C* hits 3 SSTables on disk instead of just one, > although it has the min/max column meta data to decide which SSTable contains > the most recent data. > Funny enough, if we add a clause on the clustering column to the select, this > time C* optimizes the read path: > {code} > cqlsh:test> SELECT * FROM test WHERE id=1 AND col > 25 LIMIT 1; > activity | > timestamp | source | source_elapsed > ---------------------------------------------------------------------------+--------------+-----------+---------------- > execute_cql3_query | > 23:52:31,888 | 127.0.0.1 | 0 > Parsing SELECT * FROM test WHERE id=1 AND col > 25 LIMIT 1; | > 23:52:31,888 | 127.0.0.1 | 60 > Preparing statement | > 23:52:31,888 | 127.0.0.1 | 277 > Executing single-partition query on test | > 23:52:31,889 | 127.0.0.1 | 961 > Acquiring sstable references | > 23:52:31,889 | 127.0.0.1 | 971 > Merging memtable tombstones | > 23:52:31,889 | 127.0.0.1 | 1020 > Key cache hit for sstable 3 | > 23:52:31,889 | 127.0.0.1 | 1108 > Seeking to partition beginning in data file | > 23:52:31,889 | 127.0.0.1 | 1117 > Skipped 2/3 non-slice-intersecting sstables, included 0 due to tombstones | > 23:52:31,889 | 127.0.0.1 | 1611 > Merging data from memtables and 1 sstables | > 23:52:31,890 | 127.0.0.1 | 1624 > Read 1 live and 0 tombstoned cells | > 23:52:31,890 | 127.0.0.1 | 1700 > Request complete | > 23:52:31,890 | 127.0.0.1 | 2140 > {code} -- This message was sent by Atlassian JIRA (v6.3.4#6332)