Cassandra - Write doesn't fail, but values aren't inserted

问题

I have a cluster of 3 Cassandra 2.0 nodes. My application I wrote a test which tries to write and read some data into/from Cassandra. In general this works fine.

The curiosity is that after I restarted my computer, this test will fail, because after writting I read the same value I´ve write before and there I get null instead of the value, but the was no exception while writing. If I manually truncate the used column family, the test will pass. After that I can execute this test how often I want, it passes again and again. Furthermore it doesn´t matter if there are values in the Cassandra or not. The result is alwalys the same.

If I look at the CLI and the CQL-shell there are two different views:

Does anyone have an ideas what is going wrong? The timestamp in the CLI is updated after re-execution, so it seems to be a read-problem?

A part of my code: For inserts I tried

Insert.Options insert =   QueryBuilder.insertInto(KEYSPACE_NAME,TABLENAME)
                .value(ID, id)
                .value(JAHR, zonedDateTime.getYear())
                .value(MONAT, zonedDateTime.getMonthValue())
                .value(ZEITPUNKT, date)
                .value(WERT, entry.getValue())
                .using(timestamp(System.nanoTime() / 1000));

and

Insert insert = QueryBuilder.insertInto(KEYSPACE_NAME,TABLENAME)
                .value(ID, id)
                .value(JAHR, zonedDateTime.getYear())
                .value(MONAT, zonedDateTime.getMonthValue())
                .value(ZEITPUNKT, date)
                .value(WERT, entry.getValue());

My select looks like

Select.Where select = QueryBuilder.select(WERT)
            .from(KEYSPACE_NAME,TABLENAME)
            .where(eq(ID, id))
            .and(eq(JAHR, zonedDateTime.getYear()))
            .and(eq(MONAT, zonedDateTime.getMonthValue()))
            .and(eq(ZEITPUNKT, Date.from(instant)));

Consistencylevel is QUORUM (for both) and replicationfactor 3

回答1:

I'd say this seems to be a problem with timestamps since a truncate solves the problem. In Cassandra last write wins and this could be a problem caused by the use of System.nanoTime() since

This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time.

...

The values returned by this method become meaningful only when the difference between two such values, obtained within the same instance of a Java virtual machine, is computed.

http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#nanoTime()

This means that the write that occured before the restart could have been performed "in the future" compared to the write after the restart. This would not fail the query, but the written value would simply not be visible due to the fact that there is a "newer" value available.

Do you have a requirement to use sub-millisecond precision for the insert timestamps? If possible I would recommend using System.currentTimeMillis() instead of nanoTime().

http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#currentTimeMillis()

If you have a requirement to use sub-millisecond precision it would be possible to use System.currentTimeMillis() with some kind of atomic counter that ranged between 0-999 and then use that as a timestamp. This would however break if multiple clients insert the same row at the same time.

来源：https://stackoverflow.com/questions/31612199/cassandra-write-doesnt-fail-but-values-arent-inserted