Could my large amount of tables (2k+) be causing my write timeout exceptions?

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I'm running OS Cassandra 3.11.9 with Datastax Java Driver 3.8.0. I have a Cassandra keyspace that has multiple tables functioning as lookup tables / search indices. Whenever I receive a new POST request to my endpoint, I parse the object and insert it in the corresponding Cassandra table. I also put inserts to each corresponding lookup table. (10-20 per object)

When ingesting a lot of data into the system, I've been running into WriteTimeoutExceptions in the driver.

I tried to serialize the insert requests into the lookup tables by introducing Apache Camel and putting all the Statements into a queue that the Session could work off of, but it did not help. With Camel, since the exceptions are now happening in the Camel thread, the test continues to run, instead of failing on the first exception. Eventually, the test seems to crash Cassandra. (Nothing in the Cassandra logs though)

I also tried to turn off my lookup tables and instead insert into the main table 15x per object (to simulate a similar number of writes as if I had the lookup tables on). This test passed with no exception, which makes me think the large number of tables is the problem.

Is a large number (2k+) of Cassandra tables a code smell? Should we rearchitect or just throw more resources at it? Nothing indicative has shown in the logs, mostly just some status about the number of tables etc - no exceptions)

Can the Datastax Java Driver be used multithreaded like this? It says it is threadsafe.

datastax-java-driver cassandra
1 Answers

There is a direct effect of the high number of tables onto the performance - see this doc (the whole series is good source of information), and this blog post for more details. Basically, with ~1000 tables, you get ~20-25% degradation of performance.

That's could be a reason, not completely direct, but related. For each table, Cassandra needs to allocate memory, have a part for it in the memtable, keep information about it, etc. This specific problem could come from the blocked memtable flushes, or something like. Check the nodetool tpstats and nodetool tablestats for blocked or pending memtable flushes. It's better to setup some continuous monitoring solution, such as, metrics collector for Apache Cassandra, and and for period of time watch for the important metrics that include that information as well.

Alex_Ott_186270
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