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From "Aaron Morton (Created) (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-3510) Incorrect query results due to invalid SSTable.maxTimestamp
Date Mon, 21 Nov 2011 07:16:52 GMT
Incorrect query results due to invalid SSTable.maxTimestamp

                 Key: CASSANDRA-3510
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.0.3
            Reporter: Aaron Morton
            Priority: Critical

related to CASSANDRA-3446

(sorry this is so long, took me a bit to work through it all and there is a lot of new code
:) )
h1. Summary

SSTable.maxTimestamp for files created before 1.0 defaults to Long.MIN_VALUE, and this means
the wrong data is returned from queries. 
h2. Details 

Noticed on a cluster that was upgraded from 0.8.X to 1.X, it then had trouble similar to CASSANDRA-3446.
It was rolled back to 0.8 and the migrated to 1.0.3. 

4 Node cluster, all files upgraded to "hb" format. 

In a super CF there are situations where a get for a sub columns returns a different value
than a get for the column. .e.g. 

[default@XXX] get Users[ascii('username')]['meta']['password'];
=> (column=password, value=3130323130343130, timestamp=1307352647576000)

[default@XX] get Users[ascii('username')]['meta'];     
=> (column=password, value=3034323131303034, timestamp=1319563673493000)

The correct value is the second one. 

I added logging after line 109 in o.a.c.db.CollectionController.collectTimeOrderedData() to
log the sstable name and the file max timestamp, this is what I got:

for (SSTableReader sstable : view.sstables)
    long currentMaxTs = sstable.getMaxTimestamp();
    logger.debug(String.format("Got sstable %s and max TS %d", sstable, currentMaxTs));
    reduceNameFilter(reducedFilter, container, currentMaxTs);

DEBUG 14:08:46,012 Got sstable SSTableReader(path='/var/lib/cassandra/data/X/Users-hb-12348-Data.db')
and max TS 1321824847534000
DEBUG 14:08:47,231 Got sstable SSTableReader(path='/var/lib/cassandra/data/X/Users-hb-12346-Data.db')
and max TS 1321813380793000
DEBUG 14:08:49,879 Got sstable SSTableReader(path='/var/lib/cassandra/data/X/Users-hb-12330-Data.db')
and max TS -9223372036854775808
DEBUG 14:08:49,880 Got sstable SSTableReader(path='/var/lib/cassandra/data/X/Users-hb-12325-Data.db')
and max TS -9223372036854775808

The key I was reading is present in files 12330 and 12325, the first contains the *old / wrong*
value with timestamp 1307352647576000 above. The second contains the *new / correct* value
with timestamp 1319563673493000.

When CollectionController.collectTimeOrderedData() processes the 12325 file (after processing
the 12330 file) while looping over the sstables the call to reduceNameFilter() removes the
column  from the filter because the column read from the 12330 file has a time stamp of 1307352647576000
and the 12325 file incorrectly has a max time stamp of -9223372036854775808 .

SSTableMetadata is reading the max time stamp from the stats file, but it is Long.MIN_VALUE.
I think this happens because scrub creates the SSTableWriter using cfs.createCompactionWriter()
which sets the maxTimestamp in the meta data collector according to the maxTimestamp in the
meta data for the file(s) that will be scrubbed / compacted. But for pre 1.0 format files
the default in SSTableMetadata is Long.MIN_VALUE, (see SSTableMetaData.deserialize() and the
ctor). So scrubbing a pre 1.0 file will write stats files that have maxTimestamp as Long.MIN_VALUE.

During scrubbing the SSTableWriter does not update the maxTimestamp because append(AbstractCompactedRow)
is called which expects the that cfs.createCompactionWriter() was able to set the correct
maxTimestamp on the meta data. Compaction also uses append(AbstractCompactedRow) so may create
an SSTable with an incorrect maxTimestamp if one of the input files started life as a pre
1.0 file and has a bad maxTimestamp. 

It looks like the only time the maxTimestamp is calculated is when the SSTable is originally
written. So the error from the old files will be carried along. 

e.g. If the files a,b and c have the maxTimestamps 10, 100 and Long.MIN_VALUE compaction will
write a SSTable with maxTimestamp 100. However file c may actually contain columns with a
timestamp > 100 which will be in the compacted file.

h1. Reproduce

1. Start a clean 0.8.7

2. Add a schema (details of the schema do not matter):
[default@unknown] create keyspace dev;   
Waiting for schema agreement...
... schemas agree across the cluster
[default@unknown] use dev;
Authenticated to keyspace: dev
[default@dev] create column family super_dev with column_type = 'Super' 
...	and key_validation_class = 'AsciiType' and comparator = 'AsciiType' and 
...	subcomparator = 'AsciiType' and default_validation_class = 'AsciiType';
Waiting for schema agreement...
... schemas agree across the cluster

3. Shutdown 0.8.7

4. Start 1.0.3 using the same data. Check the schema version loaded, example below shows the
wrong schema is loaded. I stepped the code and the wrong value was read from Migration.getLastMigrationId()
due to this bug. 

 INFO [main] 2011-11-21 19:39:08,546 (line 501) Loading schema version

5. Check the schema using the 1.0.3 CLI 

[default@unknown] use dev;
Authenticated to keyspace: dev
[default@dev] describe;
Keyspace: dev:
  Replication Strategy: org.apache.cassandra.locator.NetworkTopologyStrategy
  Durable Writes: true
    Options: [datacenter1:1]
  Column Families:

6. I then did a 1.0.3 scrub and re-started. The correct schema version was read, but stepping
the code both Schema SSTables had Long.MIN_VALUE as the maxTimestamp so I think it was only
the random order of the files that made it work. 

DEBUG 19:52:30,744 Got sstable SSTableReader(path='/var/lib/cassandra/data/system/Schema-hb-4-Data.db')
and max TS -9223372036854775808
DEBUG 19:52:30,744 Got sstable SSTableReader(path='/var/lib/cassandra/data/system/Schema-hb-3-Data.db')
and max TS -9223372036854775808

h1. Fixes

Not sure, (wanted to get the ticket opened and find out if I was imagining things), guessing...

Use Long.MIN_VALUE as a magic maxTimestamp that means the value is not know. This would not
fix issues where the incorrect maxTimestamp been included in compaction. 
Looking at making scrub re-calculate the maxTimestamp.

Also wondering if the maxTimestamp should default to Long.MAX_VALUE if read from a file format
that does not support maxTimestamp ?

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