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Since NDB  does not use single-key access for ordered indexes, the counts for tot_key_reads , tot_key_inserts , tot_key_updates , tot_key_writes , and tot_key_deletes  are not incremented by ordered index operations. 

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## Note 

When using tot_key_writes , you should keep in mind that a write operation in this context updates the row if the key exists, and inserts a new row otherwise. (One use of this is in the NDB  implementation of the REPLACE  SQL statement.) 

The tot_key_refs  column shows the number of key operations refused by the LDM. Generally, such a refusal is due to duplicate keys (inserts), Key not found  errors (updates, deletes, and reads), or the operation was rejected by an interpreted program used as a predicate on the row matching the key. 

The attrinfo  and keyinfo  attributes counted by the tot_key_attrinfo_bytes  and tot_key_keyinfo_bytes  columns are attributes of an LQHKEYREQ  signal (see The NDB Communication Protocol) used to initiate a key operation by the LDM. An attrinfo  typically contains tuple field values (inserts and updates) or projection specifications (for reads); keyinfo  contains the primary or unique key needed to locate a given tuple in this schema object. 

The value shown by tot_frag_scans  includes both full scans (that examine every row) and scans of subsets. Unique indexes and BLOB  tables are never scanned, so this value, like other scan-related counts, is 0 for fragment replicas of these. 

tot_scan_rows_examined  may display less than the total number of rows in a given fragment replica, since ordered index scans can limited by bounds. In addition, a client may choose to end a scan before all potentially matching rows have been examined; this occurs when using an SQL statement containing a LIMIT  or EXISTS  clause, for example. tot_scan_rows_returned  is always less than or equal to tot_scan_rows_examined . 

tot_scan_bytes_returned  includes, in the case of pushed joins, projections returned to the DBSPJ block in the NDB kernel. 

tot_qd_frag_scans  can be effected by the setting for the MaxParallelScansPerFragment  data node configuration parameter, which limits the number of scans that may execute concurrently on a single fragment replica. 

## 23.5.14.40 The ndbinfo pgman_time_track_stats Table 

This table provides information regarding the latency of disk operations for NDB Cluster Disk Data tablespaces. 

The pgman_time_track_stats  table contains the following columns: 

• node_id 

Unique node ID of this node in the cluster 

• block_number 

Block number (from blocks  table) 

• block_instance 

Block instance number 

• upper_bound 

