NDB management client's
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
(Beginning with MySQL Cluster NDB 6.3.4:) By supplying a data placement hint when the transaction is started
You can determine which TC selection method is used for
transactions started from a given SQL node using the
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 countto be greater than
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. This is a subset of
Read count. Prior to MySQL CLuster NDB 7.0, the value of
Simple read countwas incremented at a different point in time from
Read count, which could cause it to lag behind
Read countslightly, so that it was possible that
Simple read countwas not equal to
Read countfor some reporting interval, even if all reads made during that time were in fact simple reads. In MySQL Cluster NDB 7.0 and later,
NDBuses a single signal (
TCKEYREQ) containing all information necessary to forward the request, so these counts should no longer appear to be misaligned in such cases.
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
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 Operationscan 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 5.3.6, “Defining MySQL 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 countcan sometimes be greater than
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 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.
A single transaction may operate on data stored in multiple LQH blocks.
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 2-replica cluster, the write to the primary replica is
recorded in the primary LQH, and the write to the backup will be
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
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 a MySQL Cluster. This scheduler runs in an infinite loop; during each loop the scheduler performs the following tasks:
Read any incoming messages from sockets into a job buffer.
Check whether there are any timed messages to be executed; if so, put these into the job buffer as well.
Execute (in a loop) any messages in the job buffer.
Send any distributed messages that were generated by executing the messages in the job buffer.
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
ALL CLUSTERLOG STATISTICS=15
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 MySQL Cluster.
For more information about MySQL Cluster management client commands relating to logging and reporting, see Section 7.6.1, “MySQL Cluster Logging Management Commands”.