Changes in MySQL NDB Cluster 7.3.6 (5.6.19-ndb-7.3.6) (2014-07-11, General Availability)

• Functionality Added or Changed

• Bugs Fixed

Functionality Added or Changed

• NDB Cluster APIs: Added as an aid to debugging the ability to specify a human-readable name for a given Ndb object and later to retrieve it. These operations are implemented, respectively, as the setNdbObjectName() and getNdbObjectName() methods.

  To make tracing of event handling between a user application and NDB easier, you can use the reference (from getReference() followed by the name (if provided) in printouts; the reference ties together the application Ndb object, the event buffer, and the NDB storage engine's SUMA block. (Bug #18419907)

Bugs Fixed

• NDB Disk Data: Setting the undo buffer size used by InitialLogFileGroup to a value greater than that set by SharedGlobalMemory prevented data nodes from starting; the data nodes failed with Error 1504 Out of logbuffer memory. While the failure itself is expected behavior, the error message did not provide sufficient information to diagnose the actual source of the problem; now in such cases, a more specific error message Out of logbuffer memory (specify smaller undo_buffer_size or increase SharedGlobalMemory) is supplied. (Bug #11762867, Bug #55515)

• NDB Cluster APIs: When two tables had different foreign keys with the same name, ndb_restore considered this a name conflict and failed to restore the schema. As a result of this fix, a slash character (/) is now expressly disallowed in foreign key names, and the naming format parent_id/child_id/fk_name is now enforced by the NDB API. (Bug #18824753)

• NDB Cluster APIs: When an NDB data node indicates a buffer overflow via an empty epoch, the event buffer places an inconsistent data event in the event queue. When this was consumed, it was not removed from the event queue as expected, causing subsequent nextEvent() calls to return 0. This caused event consumption to stall because the inconsistency remained flagged forever, while event data accumulated in the queue.

  Event data belonging to an empty inconsistent epoch can be found either at the beginning or somewhere in the middle. pollEvents() returns 0 for the first case. This fix handles the second case: calling nextEvent() call dequeues the inconsistent event before it returns. In order to benefit from this fix, user applications must call nextEvent() even when pollEvents() returns 0. (Bug #18716991)

• NDB Cluster APIs: The pollEvents() method returned 1, even when called with a wait time equal to 0, and there were no events waiting in the queue. Now in such cases it returns 0 as expected. (Bug #18703871)

• Processing a NODE_FAILREP signal that contained an invalid node ID could cause a data node to fail. (Bug #18993037, Bug #73015)

  References: This issue is a regression of: Bug #16007980.

• When building out of source, some files were written to the source directory instead of the build dir. These included the manifest.mf files used for creating ClusterJ jars and the pom.xml file used by mvn_install_ndbjtie.sh. In addition, ndbinfo.sql was written to the build directory, but marked as output to the source directory in CMakeLists.txt. (Bug #18889568, Bug #72843)

• When the binary log injector thread commits an epoch to the binary log and this causes the log file to reach maximum size, it may need to rotate the binary log. The rotation is not performed until either all the committed transactions from all client threads are flushed to the binary log, or a maximum of 30 seconds has elapsed. In the case where all transactions were committed prior to the 30-second wait, it was possible for committed transactions from multiple client threads to belong to newer epochs than the latest epoch committed by the injector thread, causing the thread to deadlock with itself, and causing an unnecessary 30-second delay before breaking the deadlock. (Bug #18845822)

• Adding a foreign key failed with NDB Error 208 if the parent index was parent table's primary key, the primary key was not on the table's initial attributes, and the child table was not empty. (Bug #18825966)

• When an NDB table served as both the parent table and a child table for 2 different foreign keys having the same name, dropping the foreign key on the child table could cause the foreign key on the parent table to be dropped instead, leading to a situation in which it was impossible to drop the remaining foreign key. This situation can be modelled using the following CREATE TABLE statements:

  CREATE TABLE parent (
      id INT NOT NULL,
      PRIMARY KEY (id)
  ) ENGINE=NDB;
  
  CREATE TABLE child (
      id INT NOT NULL,
      parent_id INT,
      PRIMARY KEY (id),
      INDEX par_ind (parent_id),
  
      FOREIGN KEY (parent_id)
      REFERENCES parent(id)
  ) ENGINE=NDB;
  
  CREATE TABLE grandchild (
      id INT,
      parent_id INT,
      INDEX par_ind (parent_id),
  
      FOREIGN KEY (parent_id)
      REFERENCES child(id)
  ) ENGINE=NDB;

  With the tables created as just shown, the issue occured when executing the statement ALTER TABLE child DROP FOREIGN KEY parent_id, because it was possible in some cases for NDB to drop the foreign key from the grandchild table instead. When this happened, any subsequent attempt to drop the foreign key from either the child or from the grandchild table failed. (Bug #18662582)

• It was possible for a data node restart to become stuck indefinitely in start phase 101 (see Summary of NDB Cluster Start Phases) when there were connection problems between the node being restarted and one or more subscribing API nodes.

  To help prevent this from happening, a new data node configuration parameter RestartSubscriberConnectTimeout has been introduced, which can be used to control how long a data node restart can stall in start phase 101 before giving up and attempting to restart again. The default is 12000 ms. (Bug #18599198)

• Executing ALTER TABLE ... REORGANIZE PARTITION after increasing the number of data nodes in the cluster from 4 to 16 led to a crash of the data nodes. This issue was shown to be a regression caused by previous fix which added a new dump handler using a dump code that was already in use (7019), which caused the command to execute two different handlers with different semantics. The new handler was assigned a new DUMP code (7024). (Bug #18550318)

  References: This issue is a regression of: Bug #14220269.

• Following a long series of inserts, when running with a relatively small redo log and an insufficient large value for MaxNoOfConcurrentTransactions, there remained transactions that were blocked by the lack of redo log and were thus not aborted in the correct state (waiting for prepare log to be sent to disk, or LOG_QUEUED state). This caused the redo log to remain blocked until unblocked by a completion of a local checkpoint. This could lead to a deadlock, when the blocked aborts in turned blocked global checkpoints, and blocked GCPs block LCPs. To prevent this situation from arising, we now abort immediately when we reach the LOG_QUEUED state in the abort state handler. (Bug #18533982)

• ndbmtd supports multiple parallel receiver threads, each of which performs signal reception for a subset of the remote node connections (transporters) with the mapping of remote_nodes to receiver threads decided at node startup. Connection control is managed by the multi-instance TRPMAN block, which is organized as a proxy and workers, and each receiver thread has a TRPMAN worker running locally.

  The QMGR block sends signals to TRPMAN to enable and disable communications with remote nodes. These signals are sent to the TRPMAN proxy, which forwards them to the workers. The workers themselves decide whether to act on signals, based on the set of remote nodes they manage.

  The current issue arises because the mechanism used by the TRPMAN workers for determining which connections they are responsible for was implemented in such a way that each worker thought it was responsible for all connections. This resulted in the TRPMAN actions for OPEN_COMORD, ENABLE_COMREQ, and CLOSE_COMREQ being processed multiple times.

  The fix keeps TRPMAN instances (receiver threads) executing OPEN_COMORD, ENABLE_COMREQ and CLOSE_COMREQ requests. In addition, the correct TRPMAN instance is now chosen when routing from this instance for a specific remote connection. (Bug #18518037)

• During data node failure handling, the transaction coordinator performing takeover gathers all known state information for any failed TC instance transactions, determines whether each transaction has been committed or aborted, and informs any involved API nodes so that they can report this accurately to their clients. The TC instance provides this information by sending TCKEY_FAILREF or TCKEY_FAILCONF signals to the API nodes as appropriate top each affected transaction.

  In the event that this TC instance does not have a direct connection to the API node, it attempts to deliver the signal by routing it through another data node in the same node group as the failing TC, and sends a GSN_TCKEY_FAILREFCONF_R signal to TC block instance 0 in that data node. A problem arose in the case of multiple transaction cooridnators, when this TC instance did not have a signal handler for such signals, which led it to fail.

  This issue has been corrected by adding a handler to the TC proxy block which in such cases forwards the signal to one of the local TC worker instances, which in turn attempts to forward the signal on to the API node. (Bug #18455971)

• When running with a very slow main thread, and one or more transaction coordinator threads, on different CPUs, it was possible to encounter a timeout when sending a DIH_SCAN_GET_NODESREQ signal, which could lead to a crash of the data node. Now in such cases the timeout is avoided. (Bug #18449222)

• Failure of multiple nodes while using ndbmtd with multiple TC threads was not handled gracefully under a moderate amount of traffic, which could in some cases lead to an unplanned shutdown of the cluster. (Bug #18069334)

• A local checkpoint (LCP) is tracked using a global LCP state (c_lcpState), and each NDB table has a status indicator which indicates the LCP status of that table (tabLcpStatus). If the global LCP state is LCP_STATUS_IDLE, then all the tables should have an LCP status of TLS_COMPLETED.

  When an LCP starts, the global LCP status is LCP_INIT_TABLES and the thread starts setting all the NDB tables to TLS_ACTIVE. If any tables are not ready for LCP, the LCP initialization procedure continues with CONTINUEB signals until all tables have become available and been marked TLS_ACTIVE. When this initialization is complete, the global LCP status is set to LCP_STATUS_ACTIVE.

  This bug occurred when the following conditions were met:

  • An LCP was in the LCP_INIT_TABLES state, and some but not all tables had been set to TLS_ACTIVE.

  • The master node failed before the global LCP state changed to LCP_STATUS_ACTIVE; that is, before the LCP could finish processing all tables.

  • The NODE_FAILREP signal resulting from the node failure was processed before the final CONTINUEB signal from the LCP initialization process, so that the node failure was processed while the LCP remained in the LCP_INIT_TABLES state.

  Following master node failure and selection of a new one, the new master queries the remaining nodes with a MASTER_LCPREQ signal to determine the state of the LCP. At this point, since the LCP status was LCP_INIT_TABLES, the LCP status was reset to LCP_STATUS_IDLE. However, the LCP status of the tables was not modified, so there remained tables with TLS_ACTIVE. Afterwards, the failed node is removed from the LCP. If the LCP status of a given table is TLS_ACTIVE, there is a check that the global LCP status is not LCP_STATUS_IDLE; this check failed and caused the data node to fail.

  Now the MASTER_LCPREQ handler ensures that the tabLcpStatus for all tables is updated to TLS_COMPLETED when the global LCP status is changed to LCP_STATUS_IDLE. (Bug #18044717)

• When performing a copying ALTER TABLE operation, mysqld creates a new copy of the table to be altered. This intermediate table, which is given a name bearing the prefix #sql-, has an updated schema but contains no data. mysqld then copies the data from the original table to this intermediate table, drops the original table, and finally renames the intermediate table with the name of the original table.

  mysqld regards such a table as a temporary table and does not include it in the output from SHOW TABLES; mysqldump also ignores an intermediate table. However, NDB sees no difference between such an intermediate table and any other table. This difference in how intermediate tables are viewed by mysqld (and MySQL client programs) and by the NDB storage engine can give rise to problems when performing a backup and restore if an intermediate table existed in NDB, possibly left over from a failed ALTER TABLE that used copying. If a schema backup is performed using mysqldump and the mysql client, this table is not included. However, in the case where a data backup was done using the ndb_mgm client's BACKUP command, the intermediate table was included, and was also included by ndb_restore, which then failed due to attempting to load data into a table which was not defined in the backed up schema.

  To prevent such failures from occurring, ndb_restore now by default ignores intermediate tables created during ALTER TABLE operations (that is, tables whose names begin with the prefix #sql-). A new option --exclude-intermediate-sql-tables is added that makes it possible to override the new behavior. The option's default value is TRUE; to cause ndb_restore to revert to the old behavior and to attempt to restore intermediate tables, set this option to FALSE. (Bug #17882305)

• The logging of insert failures has been improved. This is intended to help diagnose occasional issues seen when writing to the mysql.ndb_binlog_index table. (Bug #17461625)

• The DEFINER column in the INFORMATION_SCHEMA.VIEWS table contained erroneous values for views contained in the ndbinfo information database. This could be seen in the result of a query such as SELECT TABLE_NAME, DEFINER FROM INFORMATION_SCHEMA.VIEWS WHERE TABLE_SCHEMA='ndbinfo'. (Bug #17018500)

• Employing a CHAR column that used the UTF8 character set as a table's primary key column led to node failure when restarting data nodes. Attempting to restore a table with such a primary key also caused ndb_restore to fail. (Bug #16895311, Bug #68893)

• The --order (-o) option for the ndb_select_all utility worked only when specified as the last option, and did not work with an equals sign.

  As part of this fix, the program's --help output was also aligned with the --order option's correct behavior. (Bug #64426, Bug #16374870)