126.96.36.199 The ndbinfo operations_per_fragment Table
operations_per_fragment table provides information about the operations performed on individual fragments and fragment replicas, as well as about some of the results from these operations.
operations_per_fragment table contains the following columns:
Name of this fragment
Name of this fragment's parent
Type of object; see text for possible values
Table ID for this table
Node ID for this node
Kernel block instance ID
Fragment ID (number)
Total number of key reads for this fragment replica
Total number of key inserts for this fragment replica
total number of key updates for this fragment replica
Total number of key writes for this fragment replica
Total number of key deletes for this fragment replica
Number of key operations refused
Total size of all
Total size of all
Total size of all interpreted programs carried by
Total number of instructions executed by interpreted programs for key operations
Total size of all data and metadata returned from key read operations
Total number of scans performed on this fragment replica
Total number of rows examined by scans
Total number of rows returned to client
Total size of data and metadata returned to the client
Total size of interpreted programs for scan operations
Total size of all bounds used in ordered index scans
Total number of instructions executed for scans
Number of times that scans of this fragment replica have been queued
Number of scans currently active on this fragment replica (excluding queued scans)
Number of scans currently queued for this fragment replica
Total number of row changes committed to this fragment replica
fq_name contains the fully qualified name of the schema object to which this fragment replica belongs. This currently has the following formats:
$unique suffix shown for unique indexes is added by mysqld; for an index created by a different NDB API client application, this may differ, or not be present.
The syntax just shown for fully qualified object names is an internal interface which is subject to change in future releases.
Consider a table
t1 created and modified by the following SQL statements:
CREATE DATABASE mydb; USE mydb; CREATE TABLE t1 ( a INT NOT NULL, b INT NOT NULL, t TEXT NOT NULL, PRIMARY KEY (b) ) ENGINE=ndbcluster; CREATE UNIQUE INDEX ix1 ON t1(b) USING HASH;
t1 is assigned table ID 11, this yields the
fq_name values shown here:
Ordered index (primary key):
For indexes or
BLOB tables, the
parent_fq_name column contains the
fq_name of the corresponding base table. For base tables, this column is always
type column shows the schema object type used for this fragment, which can take any one of the values
Unique hash index, or
BLOB tables are shown as
table_id column value is unique at any given time, but can be reused if the corresponding object has been deleted. The same ID can be seen using the ndb_show_tables utility.
block_instance column shows which LDM instance this fragment replica belongs to. You can use this to obtain information about specific threads from the
threadblocks table. The first such instance is always numbered 0.
Since there are typically two replicas, and assuming that this is so, each
fragment_num value should appear twice in the table, on two different data nodes from the same node group.
NDB does not use single-key access for ordered indexes, the counts for
tot_key_deletes are not incremented by ordered index operations.
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.)
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.
keyinfo attributes counted by the
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
EXISTS clause, for example.
tot_scan_rows_returned is always less than or equal to
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.