Oracle 5.0, Справочное руководство

Страница: 1582 / 3232

MySQL Cluster Configuration Files
1562
handled by the system.
MaxNoOfConcurrentTransactions
sets the number of parallel transactions
possible in a node.
MaxNoOfConcurrentOperations
sets the number of records that can be in
update phase or locked simultaneously.
Both of these parameters (especially
MaxNoOfConcurrentOperations
) are likely targets for users
setting specific values and not using the default value. The default value is set for systems using small
transactions, to ensure that these do not use excessive memory.
•
MaxNoOfConcurrentTransactions
Effective Version Type/Units Default Range/Values
MySQL 5.0.0 integer 4096 32 - 4G
Restart Type: S
Each cluster data node requires a transaction record for each active transaction in the cluster. The
task of coordinating transactions is distributed among all of the data nodes. The total number of
transaction records in the cluster is the number of transactions in any given node times the number
of nodes in the cluster.
Transaction records are allocated to individual MySQL servers. Each connection to a MySQL server
requires at least one transaction record, plus an additional transaction object per table accessed by
that connection. This means that a reasonable minimum for this parameter is
MaxNoOfConcurrentTransactions =
(maximum number of tables accessed in any single trans 1)
* number of cluster SQL nodes
Suppose that there are 10 SQL nodes using the cluster. A single join involving 10 tables requires
11 transaction records; if there are 10 such joins in a transaction, then 10 * 11 = 110 transaction
records are required for this transaction, per MySQL server, or 110 * 10 = 1100 transaction
records total. Each data node can be expected to handle TotalNoOfConcurrentTransactions /
number of data nodes. For a MySQL Cluster having 4 data nodes, this would mean setting
MaxNoOfConcurrentTransactions
on each data node to 1100 / 4 = 275. In addition, you should
provide for failure recovery by insuring that a single node group can accommodate all concurrent
transactions; in other words, that each data node's MaxNoOfConcurrentTransactions is sufficient to
cover a number of transaction equal to TotalNoOfConcurrentTransactions / number of node groups.
If this cluster has a single node group, then
MaxNoOfConcurrentTransactions
should be set to
1100 (the same as the total number of concurrent transactions for the entire cluster).
In addition, each transaction involves at least one operation; for this reason, the value set
for
MaxNoOfConcurrentTransactions
should always be no more than the value of
MaxNoOfConcurrentOperations
[1562] .
This parameter must be set to the same value for all cluster data nodes. This is due to the fact that,
when a data node fails, the oldest surviving node re-creates the transaction state of all transactions
that were ongoing in the failed node.
Changing the value of
MaxNoOfConcurrentTransactions
requires a complete shutdown and
restart of the cluster.
The default value is 4096.
•
MaxNoOfConcurrentOperations
Effective Version Type/Units Default Range/Values
MySQL 5.0.0 integer 32K 32 - 4G
Restart Type: N