Memory Consumption Controls

The configuration parameter memory_limit has been enhanced to control memory consumption and prevent Replication Server from automatically shutting down when it exceeds the defined value of available memory. A new configuration parameter, memory_control, manages the memory control behavior of threads in Replication Server.

With version 15.7, you can configure Replication Server to show warning messages when the memory consumption exceeds a defined threshold percentage of the total available memory. Two new configurable parameters support this enhanced memory management:

mem_warning_thr1 – specifies the threshold percentage of the total memory used before the first warning message is generated.

Default: 80% of memory_limit value.

Range: 1 – 100.
mem_warning_thr2 – specifies the threshold percentage of the total memory used before the second warning message is generated.

Default: 90% of memory_limit value.

Range: 1 – 100.

In addition, Replication Server 15.7 also addresses the issue of automatic shutdown of Replication Server when it exceeds the available memory defined by memory_limit. In Replication Server, the threads that require significant amount of memory are:

DSI
EXEC
SQT

In version 15.7, these threads execute memory control by performing a memory usage check before receiving or processing new data. During memory control, if the memory usage is found to be high, thread functioning is adjusted by:

Stopping the thread from grouping new data, and cleaning and processing existing data; or,
Making the thread go into a sleep mode such that it does not receive new data until memory is available.

There are three new server-level configuration parameters for managing flow control in EXEC, DST, and SQT threads:

mem_thr_dsi – specifies the percentage of the total memory used to force the DSI thread to stop populating the SQT cache.

Default: 80% of memory_limit value.
mem_thr_exec – specifies the percentage of the total memory used to force the EXEC thread to stop receiving commands from RepAgent.

Default: 90% of memory_limit value.
mem_thr_sqt – specifies the percentage of the total memory used to force the SQT thread to flush the largest transaction from its cache.

Default: 85% of memory_limit value.

A new server-level configuration parameter, memory_control, manages the memory control behavior of threads. Valid values for memory_control are enable (the default value) or disable. In this way, Replication Server controls the memory consumption and does not shut down because of memory issues.

Use configure replication server to alter the default values for the new configuration parameters. Use admin config to view the default or existing values.

See:

Replication Server Reference Manual > Replication Server Commands > configure replication server
Replication Server Administration Guide Volume 2 > Performance Tuning > Configuration Parameters that Affect Performance > Replication Server Parameters that Affect Performance

Monitor Thread Information

Use admin who to provide information on the memory control behavior of the thread:

State	Description
Controlling Mem	The thread is executing memory control.
Sleeping For Mem	The thread is sleeping until memory is available.

See Replication Server Reference Manual > Replication Server Commands > admin who.

Memory Management Statistics

Use admin stats to view the memory management statistics. Memory counters are enabled in the rsh module. To report the memory counters, use:

admin stats,rsh display_name instance_id

where:

display_name – is the name of a counter. Use rs_helpcounter to obtain valid display names. display_name is used only with module_name.
instance_id – identifies a particular instance of a module such as SQT or SQM. To view instance IDs, execute admin who and view the Info column. For rsh module, the SPID must be used. To view SPID, execute admin who and view the Spid column.

See Replication Server Reference Manual > Replication Server Commands > admin stats.