MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4
The NDB kernel employs a unified send buffer
whose memory is allocated dynamically from a pool shared by all
transporters. This means that the size of the send buffer can be
adjusted as necessary. Configuration of the unified send buffer
can accomplished by setting the following parameters:
TotalSendBufferMemory.
This parameter can be set for all types of NDB Cluster
nodes—that is, it can be set in the
[ndbd], [mgm], and
[api] (or [mysql])
sections of the config.ini file. It
represents the total amount of memory (in bytes) to be
allocated by each node for which it is set for use among
all configured transporters. If set, its minimum is 256KB;
the maximum is 4294967039.
To be backward-compatible with existing configurations, this parameter takes as its default value the sum of the maximum send buffer sizes of all configured transporters, plus an additional 32KB (one page) per transporter. The maximum depends on the type of transporter, as shown in the following table:
Table 25.22 Transporter types with maximum send buffer sizes
| Transporter | Maximum Send Buffer Size (bytes) |
|---|---|
| TCP | SendBufferMemory (default = 2M) |
| SHM | 20K |
This enables existing configurations to function in close to the same way as they did with NDB Cluster 6.3 and earlier, with the same amount of memory and send buffer space available to each transporter. However, memory that is unused by one transporter is not available to other transporters.
OverloadLimit.
This parameter is used in the
config.ini file
[tcp] section, and denotes the amount
of unsent data (in bytes) that must be present in the send
buffer before the connection is considered overloaded.
When such an overload condition occurs, transactions that
affect the overloaded connection fail with NDB API Error
1218 (Send Buffers overloaded in NDB
kernel) until the overload status passes. The
default value is 0, in which case the effective overload
limit is calculated as SendBufferMemory *
0.8 for a given connection. The maximum value
for this parameter is 4G.
SendBufferMemory.
This value denotes a hard limit for the amount of memory
that may be used by a single transporter out of the entire
pool specified by
TotalSendBufferMemory.
However, the sum of SendBufferMemory
for all configured transporters may be greater than the
TotalSendBufferMemory
that is set for a given node. This is a way to save memory
when many nodes are in use, as long as the maximum amount
of memory is never required by all transporters at the
same time.
You can use the
ndbinfo.transporters table to
monitor send buffer memory usage, and to detect slowdown and
overload conditions that can adversely affect performance.