The following improvements to NDB Cluster have been made in NDB Cluster 7.4:
Conflict detection and resolution enhancements. A reserved column name namespace
NDB$is now employed for exceptions table metacolumns, allowing an arbitrary subset of main table columns to be recorded, even if they are not part of the original table's primary key.
Recording the complete original primary key is no longer required, due to the fact that matching against exceptions table columns is now done by name and type only. It is now also possible for you to record values of columns which not are part of the main table's primary key in the exceptions table.
Read conflict detection is now possible. All rows read by the conflicting transaction are flagged, and logged in the exceptions table. Rows inserted in the same transaction are not included among the rows read or logged. This read tracking depends on the slave having an exclusive read lock which requires setting
ndb_log_exclusive_readsin advance. See Read conflict detection and resolution, for more information and examples.
Existing exceptions tables remain supported. For more information, see Section 8.11, “NDB Cluster Replication Conflict Resolution”.
Circular (“active-active”) replication improvements. When using a circular or “active-active” NDB Cluster Replication topology, you can assign one of the roles of primary of secondary to a given NDB Cluster using the
ndb_slave_conflict_roleserver system variable, which can be employed when failing over from an NDB Cluster acting as primary, or when using conflict detection and resolution with
NDB$EPOCH2_TRANS()(NDB 7.4.2 and later), which support delete-delete conflict handling.
See the description of the
ndb_slave_conflict_rolevariable, as well as NDB$EPOCH2(), for more information. See also Section 8.11, “NDB Cluster Replication Conflict Resolution”.
Per-fragment memory usage reporting. You can now obtain data about memory usage by individual NDB Cluster fragments from the
memory_per_fragmentview, added in NDB 7.4.1 to the
ndbinfoinformation database. For more information, see Section 7.10.17, “The ndbinfo memory_per_fragment Table”.
Node restart improvements. NDB Cluster 7.4 includes a number of improvements which decrease the time needed for data nodes to be restarted. These are described in the following list:
Memory allocated that is allocated on node startup cannot be used until it has been touched, which causes the operating system to set aside the actual physical memory required. In previous versions of NDB Cluster, the process of touching each page of memory that was allocated was singlethreaded, which made it relatively time-consuming. This process has now been reimplimented with multithreading. In tests with 16 threads, touch times on the order of 3 times shorter than with a single thread were observed.
Increased parallelization of local checkpoints; in NDB Cluster 7.4, LCPs now support 32 fragments rather than 2 as before. This greatly increases utilization of CPU power that would otherwise go unused, and can make LCPs faster by up to a factor of 10; this speedup in turn can greatly improve node restart times.
The degree of parallelization used for the node copy phase during node and system restarts can be controlled in NDB 7.4.3 and later by setting the
MaxParallelCopyInstancesdata node configuration parameter to a nonzero value.
Reporting on disk writes is provided by new
disk_write_speed_aggregate_node, which provide information about the speed of disk writes for each LDM thread that is in use.
This release also adds the data node configuration parameters
MaxDiskWriteSpeedOwnRestartto control write speeds for LCPs and backups when the present node, another node, or no node is currently restarting.
These changes are intended to supersede configuration of disk writes using the
DiskCheckpointSpeedInRestartconfiguration parameters. These 2 parameters have now been deprecated, and are subject to removal in a future NDB Cluster release.
Faster times for restoring an NDB Cluster from backup have been obtained by replacing delayed signals found at a point which was found to be critical to performance with normal (undelayed) signals. The elimination or replacement of these unnecessary delayed signals should noticeably reduce the amount of time required to back up an NDB Cluster, or to restore an NDB Cluster from backup.
Several internal methods relating to the
NDBreceive thread have been optimized, to increase the efficiency of SQL processing by
NDB. The receiver thread at time may have to process several million received records per second, so it is critical that it not perform unnecessary work or waste resources when retrieving records from NDB Cluster data nodes.
Improved reporting of NDB Cluster restarts and start phases. The
restart_infotable (included in the
ndbinfoinformation database beginning with NDB 7.4.2) provides current status and timing information about node and system restarts.
Reporting and logging of NDB Cluster start phases also provides more frequent and specific printouts during startup than previously. See Section 7.1, “Summary of NDB Cluster Start Phases”, for more information.
NDB API: new Event API. NDB 7.4.3 introduces an epoch-driven Event API that supercedes the earlier GCI-based model. The new version of the API also simplifies error detection and handling. These changes are realized in the NDB API by implementing a number of new methods for
NdbEventOperation, deprecating several other methods of both classes, and adding new type values to
The event handling methods added to
Ndbin NDB 7.4.3 are
isConsistentGCI()are deprecated beginning with the same release.
NDB 7.4.3 adds the
NdbEventOperationevent handling methods
isErrorEpoch; it obsoletes
While some (but not all) of the new methods are direct replacements for deprecated methods, not all of the deprecated methods map to new ones. The Event Class, provides information as to which old methods correspond to new ones.
Error handling using the new API is no longer handled using dedicated
clearError()methods, which are now deprecated (and thus subject to removal in a future release of NDB Cluster). To support this change, the list of
TableEventtypes now includes the values
TE_INCONSISTENT(inconsistent epoch), and
Improvements in event buffer management have also been made by implementing new
get_event_buffer_memory_usage()methods. Memory buffer usage can now be represented in application code using
ndb_eventbuffer_free_percentsystem variable, also implemented in NDB Cluster 7.4, makes it possible for event buffer memory usage to be checked from MySQL client applications.
Per-fragment operations information. In NDB 7.4.3 and later, counts of various types of operations on a given fragment or fragment replica can obtained easily using the
operations_per_fragmenttable in the
ndbinfoinformation database. This includes read, write, update, and delete operations, as well as scan and index operations performed by these. Information about operations refused, and about rows scanned and returned from a given fragment replica, is also shown in
operations_per_fragment. This table also provides information about interpreted programs used as attribute values, and values returned by them.
NDB Cluster 7.4 is also supported by MySQL Cluster Manager, which provides an advanced command-line interface that can simplify many complex NDB Cluster management tasks. See MySQL™ Cluster Manager 1.4.7 User Manual, for more information.