Question-: You are facing performance issue with your Cassandra cluster, specifically you observe particular node is not performing as required and facing the issue of the load balance. Which of the following command would be helpful in this case from the nodetool utility? A. gossipinfo B. info C. gcstat D. ring E. assassinate And : D Exp : “nodetool ring� provides the status and information about the ring, specially provides the idea of the load balance and if any nodes are down. Suppose your node is correctly configured it may show a different ring. Following information, you can get from the nodetool utility - It shows the info about the tokens in the ring - Cluster-level, table level from the perspective of the queried node. - It can be used to determine the balance of tokens in the cluster. - Check the load column value to determine the balance of load. - Even if you see hotspot in your ring you can utilize detail from this command output.
Admin only Question-: When you run the command “nodetool tablestats -H –keyspace_name� . The output generated is all the tables in the provided keyspace across entire cluster? A. True B. False
Answer: B Exp: First let’s understand what is the tablestats command. It is good when you wanted to check for the data modeling info. Like you are getting the correct partition key or not or is it overloading a particular node and row count information. Hence, using this command you can get the detail about a particular table on a particular node (again not entire cluster or ring). Remember this does not provide the table statistics across entire cluster.
Admin only
Question-: By using the “tablestats� command which of the following info is available to us? A. It would tell us whether the table has been flushed to disk or not. B. You can get the detail about the resources consumed by a table. C. It would give the detail, about how much overall size of the database D. It would let us know overall uptime of the Cassandra cluster.
Answer: A, B Exp: When you use the tablestats command then you would be getting the following details for a table. This does not provide information for the entire cluster. But rather point in time information for a particular table.
Keyspace: HadoopExamKS Read Count: 98787 Read Latency: 0.21 ms. Write Count: 21845 Write Latency: 0.02903473521 ms. Total number of tables: 21 ----------------------------------- Pending Flushes: 0 Table: HE_COURSES SSTable count: 2 Space used (live): 51.62 MB Space used (total): 51.62 MB Space used by snapshots (total): 0 bytes Off heap memory used (total): 302.36 KB SSTable Compression Ratio: 0.0 Number of keys (estimate): 376390 Memtable cell count: 200120 Memtable data size: 45.16 MB Memtable off heap memory used: 0 bytes Memtable switch count: 2 Local read count: 182849 Local read latency: 0.125 ms Local write count: 435355 Local write latency: 0.022 ms Pending flushes: 0 Percent repaired: 100.0% Bloom filter false positives: 11 Bloom filter false ratio: 0.00000 Bloom filter space used: 265.81 KB Bloom filter off heap memory used: 265.8 KB Index summary off heap memory used: 36.57 KB Compression metadata off heap memory used: 0 bytes Compacted partition minimum bytes: 216 bytes Compacted partition maximum bytes: 258 bytes Compacted partition mean bytes: 258 bytes Average live cells per slice (last five minutes): 1.0 Maximum live cells per slice (last five minutes): 1 Average tombstones per slice (last five minutes): 1.0 Maximum tombstones per slice (last five minutes): 1
Admin only
Question-: You are working in Acmeshell Inc. where they have node cluster setup. One of the data scientists had reported that, while querying the table they see slowness since last couple of hours. Which of the following command you would be using to check this detail? A. nodetool tablestats B. nodetool ring C. nodetool tablehistograms D. nodetool gcstats E. nodetool failuredetector
Answer: C
Explanation: Lets understand the basics of the listed command
- tablestats: Provide statistics about one or more tables. Statistics are updated after SSTables changes through compaction or flushing.
- tablehistograms : It provides the current performance statistics for read and write latency on a table during the last fifteen minutes, which includes the read/write latency, partition size, cell count, and number of SSTables. Even using this command we can analyze performance and tune individual table and ensure that the percent latency level meets the SLA for the data stored in the table.
- ring: This provide the node status and information about the ring as determined by the node being queried. And to get the detail if any node is down or what is the current load balance. If the cluster is not properly configured then different node may show a different ring.
- gcstats : It maintain the stats and tell you all the garbage collection information when the last command was run. Which will let you know that GC elapsed time (total and standard deviation) GC elapsed time, the disk space reclaimed in MB, number of GC and direct memory bytes.
- failuredetector: If there is any failure in the cluster then it can help you get that detail.