Memory management parameters

The following table describes parameters for managing Vertica memory usage.

Query the CONFIGURATION_PARAMETERS system table to determine what levels (node, session, user, database) are valid for a given parameter.

MemoryPollerIntervalSec

Specifies in seconds how often the Vertica memory poller checks whether Vertica memory usage is below the thresholds of several configuration parameters (see below):

• MemoryPollerMallocBloatThreshold

• MemoryPollerReportThreshold

• MemoryPollerTrimThreshold

Important

To disable polling of all thresholds, set this parameter to 0. Doing so effectively disables automatic memory usage reporting and trimming.

Default: 2

MemoryPollerMallocBloatThreshold

Threshold of glibc memory bloat.

The memory poller calls glibc function malloc_info() to obtain the amount of free memory in malloc. It then compares MemoryPollerMallocBloatThreshold—by default, set to 0.3—with the following expression:

free-memory-in-malloc / RSS

If this expression evaluates to a value higher than MemoryPollerMallocBloatThreshold, the memory poller calls glibc function malloc_trim(). This function reclaims free memory from malloc and returns it to the operating system. Details on calls to malloc_trim() are written to system table MEMORY_EVENTS.

To disable polling of this threshold, set the parameter to 0.

Default: 0.3

MemoryPollerReportThreshold

Threshold of memory usage that determines whether the Vertica memory poller writes a report.

The memory poller compares MemoryPollerReportThreshold with the following expression:

RSS / available-memory

When this expression evaluates to a value higher than MemoryPollerReportThreshold—by default, set to 0.93, then the memory poller writes a report to MemoryReport.log, in the Vertica working directory. This report includes information about Vertica memory pools, how much memory is consumed by individual queries and session, and so on. The memory poller also logs the report as an event in system table MEMORY_EVENTS, where it sets EVENT_TYPE to MEMORY_REPORT.

To disable polling of this threshold, set the parameter to 0.

Default: 0.93

MemoryPollerTrimThreshold

Threshold for the memory poller to start checking whether to trim glibc-allocated memory.

The memory poller compares MemoryPollerTrimThreshold—by default, set to 0.83— with the following expression:

RSS / available-memory

If this expression evaluates to a value higher than MemoryPollerTrimThreshold, then the memory poller starts checking the next threshold—set in MemoryPollerMallocBloatThreshold—for glibc memory bloat.

To disable polling of this threshold, set the parameter to 0. Doing so also disables polling of MemoryPollerMallocBloatThreshold.

Default: 0.83