New features and other important changes in NDB Cluster 7.6 which are likely to be of interest are shown in the following list:
New Disk Data table file format. A new file format was introduced in NDB 7.6.2 for NDB Disk Data tables, which makes it possible for each Disk Data table to be uniquely identified without reusing any table IDs. The format was improved further in NDB 7.6.4. This should help resolve issues with page and extent handling that were visible to the user as problems with rapid creating and dropping of Disk Data tables, and for which the old format did not provide a ready means to fix.
The new format is now used whenever new undo log file groups and tablespace data files are created. Files relating to existing Disk Data tables continue to use the old format until their tablespaces and undo log file groups are re-created.Important
The old and new formats are not compatible; different data files or undo log files that are used by the same Disk Data table or tablespace cannot use a mix of formats.
To avoid problems relating to the changes in format, you should re-create any existing tablespaces and undo log file groups when upgrading to NDB 7.6.2 or NDB 7.6.4. You can do this by performing an initial restart of each data node (that is, using the
--initialoption) as part of the upgrade process. You can expect this step to be made mandatory as part of upgrading from NDB 7.5 or an earlier release series to NDB 7.6 or later.
If you are using Disk Data tables, a downgrade from any NDB 7.6 release—without regard to release status—to any NDB 7.5 or earlier release requires that you restart all data nodes with
--initialas part of the downgrade process. This is because NDB 7.5 and earlier release series are not able to read the new Disk Data file format.
For more information, see Section 21.2.8, “Upgrading and Downgrading NDB Cluster”.
Data memory pooling and dynamic index memory. Memory required for indexes on
NDBtable columns is now allocated dynamically from that allocated for
DataMemory. For this reason, the
IndexMemoryconfiguration parameter is now deprecated, and subject to removal in a future release series.Important
Starting with NDB 7.6.2, if
IndexMemoryis set in the
config.inifile, the management server issues the warning IndexMemory is deprecated, use Number bytes on each ndbd(DB) node allocated for storing indexes instead on startup, and any memory assigned to this parameter is automatically added to
In addition, the default value for
DataMemoryhas been increased to 98M; the default for
IndexMemoryhas been decreased to 0.
The pooling together of index memory with data memory simplifies the configuration of
NDB; a further benefit of these changes is that scaling up by increasing the number of LDM threads is no longer limited by having set an insufficiently large value for
IndexMemory.This is because index memory is no longer a static quantity which is allocated only once (when the cluster starts), but can now be allocated and deallocated as required. Previously, it was sometimes the case that increasing the number of LDM threads could lead to index memory exhaustion while large amounts of
As part of this work, a number of instances of
DataMemoryusage not directly related to storage of table data now use transaction memory instead.
For this reason, it may be necessary on some systems to increase
SharedGlobalMemoryto allow transaction memory to increase when needed, such as when using NDB Cluster Replication, which requires a great deal of buffering on the data nodes. On systems performing initial bulk loads of data, it may be necessary to break up very large transactions into smaller parts.
In addition, data nodes now generate
MemoryUsageevents (see Section 184.108.40.206, “NDB Cluster Log Events”) and write appropriate messages in the cluster log when resource usage reaches 99%, as well as when it reaches 80%, 90%, or 100%, as before.
Other related changes are listed here:
REPORT MEMORYUSAGEand other commands which expose memory consumption now shows index memory consumption using 32K pages (previously these were 8K pages).
ndbinfo.resourcestable now shows the
TRANSACTION_MEMORY, and the
RESERVEDresource has been removed.
ndbinfo processes and config_nodes tables. NDB 7.6.2 adds two tables to the
ndbinfoinformation database to provide information about cluster nodes; these tables are listed here:
config_nodes: This table the node ID, process type, and host name for each node listed in an NDB cluster's configuration file.
processesshows information about nodes currently connected to the cluster; this information includes the process name and system process ID; for each data node and SQL node, it also shows the process ID of the node's angel process. In addition, the table shows a service address for each connected node; this address can be set in NDB API applications using the
Ndb_cluster_connection::set_service_uri()method, which is also added in NDB 7.6.2.
System name. The system name of an NDB cluster can be used to identify a specific cluster. Beginning with NDB 7.6.2, the MySQL Server shows this name as the value of the
Ndb_system_namestatus variable; NDB API applications can use the
Ndb_cluster_connection::get_system_name()method which is added in the same release.
A system name based on the time the management server was started is generated automatically>; you can override this value by adding a
[system]section to the cluster's configuration file and setting the
Nameparameter to a value of your choice in this section, prior to starting the management server.
ndb_import CSV import tool. ndb_import, added in in NDB Cluster 7.6.2, loads CSV-formatted data directly into an
NDBtable using the NDB API (a MySQL server is needed only to create the table and database in which it is located). ndb_import can be regarded as an analog of mysqlimport or the
LOAD DATA INFILESQL statement, and supports many of the same or similar options for formatting of the data.
Assuming that the database and target
NDBtable exist, ndb_import needs only a connection to the cluster's management server (ndb_mgmd) to perform the importation; for this reason, there must be an
[api]slot available to the tool in the cluster's
See Section 21.4.14, “ndb_import — Import CSV Data Into NDB”, for more information.
ndb_top monitoring tool. Added the ndb_top utility, which shows CPU load and usage information for an
NDBdata node in real time. This information can be displayed in text format, as an ASCII graph, or both. The graph can be shown in color, or using grayscale.
ndb_top connects to an NDB Cluster SQL node (that is, a MySQL Server). For this reason, the program must be able to connect as a MySQL user having the
SELECTprivilege on tables in the
ndb_top is available for Linux, Solaris, and Mac OS X platforms beginning with NDB 7.6.3. It is not currently available for Windows platforms.
For more information, see Section 21.4.30, “ndb_top — View CPU usage information for NDB threads”.
Code cleanup. A significant number of debugging statements and printouts not necessary for normal operations have been moved into code used only when testing or debugging
NDB, or dispensed with altogether. This removal of overhead should result in a noticeable improvement in the performance of LDM and TC threads on the order of 10% in many cases.
LDM thread and LCP improvements. Previously, when a local data mangement thread experienced I/O lag, it wrote to local checkpoints more slowly. This could happen, for example, during a disk overload condition. Problems could occur because other LDM threads did not always observe this state, or do likewise.
NDBnow tracks I/O lag mode globally, so that this state is reported as soon as at least one thread is writing in I/O lag mode; it then makes sure that the reduced write speed for this LCP is enforced for all LDM threads for the duration of the slowdown condition. Because the reduction in write speed is now observed by other LDM instances, overall capacity is increased; this enables the disk overload (or other condition inducing I/O lag) to be overcome more quickly in such cases than it was previously.
NDB error identification. Error messages and information can be obtained using the mysql client in NDB 7.6.4 and later from a new
error_messagestable in the
ndbinfoinformation database. In addition, the 7.6.4 release introduces a command-line client ndb_perror for obtaining information from NDB error codes; this replaces using perror with
--ndb, which is now deprecated and subject to removal in a future release.
For more information, see Section 220.127.116.11, “The ndbinfo error_messages Table”, and Section 21.4.17, “ndb_perror — Obtain NDB error message information”.
SPJ improvements. When executing a scan as a pushed join (that is, the root of the query is a scan), the
DBTCblock sends an SPJ request to a
DBSPJinstance on the same node as the fragment to be scanned. Formerly, one such request was sent for each of the node's fragments. As the number of
DBSPJinstances is normally set less than the number of LDM instances, this means that all SPJ instances were involved in the execution of a single query, and, in fact, some SPJ instances could (and did) receive multiple requests from the same query. In NDB 7.6.4, it becomes possible for a single SPJ request to handle a set of root fragments to be scanned, so that only a single SPJ request (
SCAN_FRAGREQ) needs to be sent to any given SPJ instance (
DBSPJblock) on each node.
DBSPJconsumes a relatively small amount of the total CPU used when evaluating a pushed join, unlike the LDM block (which is repsonsible for the majority of the CPU usage), introducing multiple SPJ blocks adds some parallelism, but the additional overhead also increases. By enabling a single SPJ request to handle a set of root fragments to be scanned, such that only a single SPJ request is sent to each
DBSPJinstance on each node and batch sizes are allocated per fragment, the multi-fragment scan can obtain a larger total batch size, allowing for some scheduling optimizations to be done within the SPJ block, which can scan a single fragment at at a time (giving it the total batch size allocation), scan all fragments in parallel using smaller sub-batches, or some combination of the two.
This work is expected to increase performance of pushed-down joins for the following reasons:
Since multiple root fragments can be scanned for each SPJ request, it is necessary to request fewer SPJ instances when executing a pushed join
Increased available batch size allocation, and for each fragment, should also in most cases result in fewer requests being needed to complete a join
Improved O_DIRECT handling for redo logs. NDB 7.6.4 implements a new data node configuration parameter
ODirectSyncFlagwhich causes completed redo log writes using
O_DIRECTto be handled as
ODirectSyncFlagis disabled by default; to enable it, set it to
You should bear in mind that the setting for this parameter is ignored when at least one of the following conditions is true:
ODirectis not enabled.
InitFragmentLogFilesis set to
Locking of CPUs to offline index build threads. In NDB 7.6.4 and later, offline index builds by default use all cores available to ndbmtd, instead of being limited to the single core reserved for the I/O thread. It also becomes possible to specify a desired set of cores to be used for I/O threads performing offline multithreaded builds of ordered indexes. This can improve restart and restore times and performance, as well as availability.Note
“Offline” as used here refers to an ordered index build that takes place while a given table is not being written to. Such index builds occur during a node or system restart, or when restoring a cluster from backup using ndb_restore
This improvement involves several related changes. The first of these is to change the default value for the
BuildIndexThreadsconfiguration parameter (from 0 to 128), means that offline ordered index builds are now multithreaded by default. The default value for the
TwoPassInitialNodeRestartCopyis also changed (from
true), so that an initial node restart first copies all data without any creation of indexes from a “live” node to the node which is being started, builds the ordered indexes offline after the data has been copied, then again synchronizes with the live node; this can significantly reduce the time required for building indexes. In addition, to facilitate explicit locking of offline index build threads to specific CPUs, a new thread type (
idxbld) is defined for the
As part of this work,
NDBcan now distinguish between execution thread types and other types of threads, and between types of threads which are permanently assigned to specific tasks, and those whose assignments are merely temporary.
For additonal information, see the descriptions of the parameters.
Variable batch sizes for DDL bulk data operations. As part of work ongoing to optimize bulk DDL performance by ndbmtd, it is now possible to obtain performance improvements by increasing the batch size for the bulk data parts of DDL operations processing data using scans. Batch sizes are now made configurable for unique index builds, foreign key builds, and online reorganization, by setting the respective data node configuration parameters listed here:
For each of the parameters just listed, the default value is 64, the minimum is 16, and the maximum is 512.
Increasing the appropriate batch size or sizes can help amortize inter-thread and inter-node latencies and make use of more parallel resources (local and remote) to help scale DDL performance. In each case there can be a tradeoff with ongoing traffic.
Partial LCPs. NDB 7.6.4 implements partial local checkpoints. Formerly, an LCP always made a copy of the entire database. When working with terabytes of data this process could require a great deal of time, with an adverse impact on node and cluster restarts especially, as well as more space for the redo logs. It is now no longer strictly necessary for LCPs to do this—instead, an LCP now by default saves only the records that have changed since the last LCP plus one fourth of all records.
As part of this change, two new data node configuration parameters are inroduced in this release:
true, or enabled) enables partial LCPs.
RecoveryWorkcontrols the percentage of space given over to LCPs; it increases with the amount of work which must be performed on LCPs during restarts as opposed to that performed during normal operations. Raising this value causes LCPs during normal operations to require writing fewer records and so decreases the usual workload. Raising this value also means that restarts can take longer.
You must disable partial LCPs explicitly by setting
EnablePartialLcp=false. This uses the least amount of disk, but also tends to maximize the write load for LCPs. To optimize for the lowest workload on LCPs during normal operation, use
RecoveryWork=100. To use the least disk space for partial LCPs, but with bounded writes, use
RecoveryWork=25, which is the minimum for
RecoveryWork. The default is
RecoveryWork=50, which means LCP files require approximately 1.5 times
CompressedLcp=1, this can be further reduced by half. Recovery times using the default settings should also be much faster than when
EnablePartialLcpis set to
In addition the data node configuration parameters
BackupMaxWriteSizeare all now deprecated, and subject to removal in a future release of MySQL NDB Cluster.
As part of this enhancement, work has been done to correct several issues with node restarts wherein it was possible to run out of undo log in various situations, most often when restoring a node that had been down for a long time during a period of intensive write activity.
Additional work was done to improve data node survival of long periods of synchronization without timing out, by updating the LCP watchdog during this process, and keeping better track of the progress of disk data synchronization. Previously, there was the possibility of spurious warnings or even node failures if synchronization took longer than the LCP watchdog timeout.
You should keep in mind, when planning for disk usage by partial LCPs, that during recovery it remains necessary to restore the database fully. This means that an initial node restart still requires a complete LCP; partial LCPs cannot be used for this purpose.Important
When upgrading an NDB Cluster that uses disk data tables to NDB 7.6.4 or downgrading it from NDB 7.6.4, it is necessary to restart all data nodes with