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Thecounters 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.

Thecounters table contains the following columns:

Notes

Each counter is associated with a particular NDB kernel block.

TheOPERATIONS counter is associated with theDBLQH (local query handler) kernel block. A primary-key read counts as one operation, as does a primary-key update. For reads, there is one operation inDBLQH per operation inDBTC. For writes, there is one operation counted per fragment replica.

TheATTRINFO,TRANSACTIONS,COMMITS,READS,LOCAL_READS,SIMPLE_READS,WRITES,LOCAL_WRITES,ABORTS,TABLE_SCANS, andRANGE_SCANS counters are associated with theDBTC (transaction co-ordinator) kernel block.

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

TheREADS 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 onceDBTC 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. SeeNDB Protocol Messages, for more information aboutATTRINFO messages in theNDB kernel.

TheLOCAL_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, andSCAN_ROWS_RETURNED counters are associated with theDBSPJ (select push-down join) kernel block.

Theblock_name andblock_instance columns provide, respectively, the applicable NDB kernel block name and instance number. You can use these to obtain information about specific threads from thethreadblocks 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: