21.6.15.10 The ndbinfo counters Table

The counters table provides running totals of events such as reads and writes for specific kernel blocks and data nodes. Counts are kept from the most recent node start or restart; a node start or restart resets all counters on that node. Not all kernel blocks have all types of counters.

The counters table contains the following columns:

• node_id

  The data node ID

• block_name

  Name of the associated NDB kernel block (see NDB Kernel Blocks).

• block_instance

  Block instance

• counter_id

  The counter's internal ID number; normally an integer between 1 and 10, inclusive.

• counter_name

  The name of the counter. See text for names of individual counters and the NDB kernel block with which each counter is associated.

• val

  The counter's value

Notes

Each counter is associated with a particular NDB kernel block.

The OPERATIONS counter is associated with the DBLQH (local query handler) kernel block (see The DBLQH Block). A primary-key read counts as one operation, as does a primary-key update. For reads, there is one operation in DBLQH per operation in DBTC. For writes, there is one operation counted per fragment replica.

The ATTRINFO, TRANSACTIONS, COMMITS, READS, LOCAL_READS, SIMPLE_READS, WRITES, LOCAL_WRITES, ABORTS, TABLE_SCANS, and RANGE_SCANS counters are associated with the DBTC (transaction co-ordinator) kernel block (see The DBTC Block).

LOCAL_WRITES and LOCAL_READS are primary-key operations using a transaction coordinator in a node that also holds the primary fragment replica of the record.

The READS counter includes all reads. LOCAL_READS includes only those reads of the primary fragment replica on the same node as this transaction coordinator. SIMPLE_READS includes only those reads in which the read operation is the beginning and ending operation for a given transaction. Simple reads do not hold locks but are part of a transaction, in that they observe uncommitted changes made by the transaction containing them but not of any other uncommitted transactions. Such reads are “simple” from the point of view of the TC block; since they hold no locks they are not durable, and once DBTC has routed them to the relevant LQH block, it holds no state for them.

ATTRINFO keeps a count of the number of times an interpreted program is sent to the data node. See NDB Protocol Messages, for more information about ATTRINFO messages in the NDB kernel.

The LOCAL_TABLE_SCANS_SENT, READS_RECEIVED, PRUNED_RANGE_SCANS_RECEIVED, RANGE_SCANS_RECEIVED, LOCAL_READS_SENT, CONST_PRUNED_RANGE_SCANS_RECEIVED, LOCAL_RANGE_SCANS_SENT, REMOTE_READS_SENT, REMOTE_RANGE_SCANS_SENT, READS_NOT_FOUND, SCAN_BATCHES_RETURNED, TABLE_SCANS_RECEIVED, and SCAN_ROWS_RETURNED counters are associated with the DBSPJ (select push-down join) kernel block (see The DBSPJ Block).

The block_name and block_instance columns provide, respectively, the applicable NDB kernel block name and instance number. You can use these to obtain information about specific threads from the threadblocks table.

A number of counters provide information about transporter overload and send buffer sizing when troubleshooting such issues. For each LQH instance, there is one instance of each counter in the following list:

• LQHKEY_OVERLOAD: Number of primary key requests rejected at the LQH block instance due to transporter overload

• LQHKEY_OVERLOAD_TC: Count of instances of LQHKEY_OVERLOAD where the TC node transporter was overloaded

• LQHKEY_OVERLOAD_READER: Count of instances of LQHKEY_OVERLOAD where the API reader (reads only) node was overloaded.

• LQHKEY_OVERLOAD_NODE_PEER: Count of instances of LQHKEY_OVERLOAD where the next backup data node (writes only) was overloaded

• LQHKEY_OVERLOAD_SUBSCRIBER: Count of instances of LQHKEY_OVERLOAD where a event subscriber (writes only) was overloaded.

• LQHSCAN_SLOWDOWNS: Count of instances where a fragment scan batch size was reduced due to scanning API transporter overload.