21.6.3.3 Using CLUSTERLOG STATISTICS in the NDB Cluster Management Client

The NDB management client's CLUSTERLOG STATISTICS command can provide a number of useful statistics in its output. Counters providing information about the state of the cluster are updated at 5-second reporting intervals by the transaction coordinator (TC) and the local query handler (LQH), and written to the cluster log.

Transaction coordinator statistics.  Each transaction has one transaction coordinator, which is chosen by one of the following methods:

• In a round-robin fashion

• By communication proximity

• By supplying a data placement hint when the transaction is started

Note

You can determine which TC selection method is used for transactions started from a given SQL node using the ndb_optimized_node_selection system variable.

All operations within the same transaction use the same transaction coordinator, which reports the following statistics:

• Trans count.  This is the number transactions started in the last interval using this TC as the transaction coordinator. Any of these transactions may have committed, have been aborted, or remain uncommitted at the end of the reporting interval.

  Note

  Transactions do not migrate between TCs.

• Commit count.  This is the number of transactions using this TC as the transaction coordinator that were committed in the last reporting interval. Because some transactions committed in this reporting interval may have started in a previous reporting interval, it is possible for Commit count to be greater than Trans count.

• Read count.  This is the number of primary key read operations using this TC as the transaction coordinator that were started in the last reporting interval, including simple reads. This count also includes reads performed as part of unique index operations. A unique index read operation generates 2 primary key read operations—1 for the hidden unique index table, and 1 for the table on which the read takes place.

• Simple read count.  This is the number of simple read operations using this TC as the transaction coordinator that were started in the last reporting interval.

• Write count.  This is the number of primary key write operations using this TC as the transaction coordinator that were started in the last reporting interval. This includes all inserts, updates, writes and deletes, as well as writes performed as part of unique index operations.

  Note

  A unique index update operation can generate multiple PK read and write operations on the index table and on the base table.

• AttrInfoCount.  This is the number of 32-bit data words received in the last reporting interval for primary key operations using this TC as the transaction coordinator. For reads, this is proportional to the number of columns requested. For inserts and updates, this is proportional to the number of columns written, and the size of their data. For delete operations, this is usually zero.

  Unique index operations generate multiple PK operations and so increase this count. However, data words sent to describe the PK operation itself, and the key information sent, are not counted here. Attribute information sent to describe columns to read for scans, or to describe ScanFilters, is also not counted in AttrInfoCount.

• Concurrent Operations.  This is the number of primary key or scan operations using this TC as the transaction coordinator that were started during the last reporting interval but that were not completed. Operations increment this counter when they are started and decrement it when they are completed; this occurs after the transaction commits. Dirty reads and writes—as well as failed operations—decrement this counter.

  The maximum value that Concurrent Operations can have is the maximum number of operations that a TC block can support; currently, this is (2 * MaxNoOfConcurrentOperations) + 16 + MaxNoOfConcurrentTransactions. (For more information about these configuration parameters, see the Transaction Parameters section of Section 21.4.3.6, “Defining NDB Cluster Data Nodes”.)

• Abort count.  This is the number of transactions using this TC as the transaction coordinator that were aborted during the last reporting interval. Because some transactions that were aborted in the last reporting interval may have started in a previous reporting interval, Abort count can sometimes be greater than Trans count.

• Scans.  This is the number of table scans using this TC as the transaction coordinator that were started during the last reporting interval. This does not include range scans (that is, ordered index scans).

• Range scans.  This is the number of ordered index scans using this TC as the transaction coordinator that were started in the last reporting interval.

• Local reads.  This is the number of primary-key read operations performed using a transaction coordinator on a node that also holds the primary fragment replica of the record. This count can also be obtained from the LOCAL_READS counter in the ndbinfo.counters table.

• Local writes.  This contains the number of primary-key read operations that were performed using a transaction coordinator on a node that also holds the primary fragment replica of the record. This count can also be obtained from the LOCAL_WRITES counter in the ndbinfo.counters table.

Local query handler statistics (Operations).  There is 1 cluster event per local query handler block (that is, 1 per data node process). Operations are recorded in the LQH where the data they are operating on resides.

Note

A single transaction may operate on data stored in multiple LQH blocks.

The Operations statistic provides the number of local operations performed by this LQH block in the last reporting interval, and includes all types of read and write operations (insert, update, write, and delete operations). This also includes operations used to replicate writes. For example, in a cluster having two fragment replicas, the write to the primary fragment replica is recorded in the primary LQH, and the write to the backup is recorded in the backup LQH. Unique key operations may result in multiple local operations; however, this does not include local operations generated as a result of a table scan or ordered index scan, which are not counted.

Process scheduler statistics.  In addition to the statistics reported by the transaction coordinator and local query handler, each ndbd process has a scheduler which also provides useful metrics relating to the performance of an NDB Cluster. This scheduler runs in an infinite loop; during each loop the scheduler performs the following tasks:

1. Read any incoming messages from sockets into a job buffer.

2. Check whether there are any timed messages to be executed; if so, put these into the job buffer as well.

3. Execute (in a loop) any messages in the job buffer.

4. Send any distributed messages that were generated by executing the messages in the job buffer.

5. Wait for any new incoming messages.

Process scheduler statistics include the following:

• Mean Loop Counter.  This is the number of loops executed in the third step from the preceding list. This statistic increases in size as the utilization of the TCP/IP buffer improves. You can use this to monitor changes in performance as you add new data node processes.

• Mean send size and Mean receive size.  These statistics enable you to gauge the efficiency of, respectively writes and reads between nodes. The values are given in bytes. Higher values mean a lower cost per byte sent or received; the maximum value is 64K.

To cause all cluster log statistics to be logged, you can use the following command in the NDB management client:

ndb_mgm> ALL CLUSTERLOG STATISTICS=15

Note

Setting the threshold for STATISTICS to 15 causes the cluster log to become very verbose, and to grow quite rapidly in size, in direct proportion to the number of cluster nodes and the amount of activity in the NDB Cluster.

For more information about NDB Cluster management client commands relating to logging and reporting, see Section 21.6.3.1, “NDB Cluster Logging Management Commands”.