segment_*

The segment_* tables of the gpperfmon database contain memory allocation statistics for the Greengage DB segment instances. They track the amount of memory consumed by all PostgreSQL processes of a particular segment instance, and the remaining amount of memory available to a segment as per the settings configured by the currently active resource management scheme (resource groups or resource queues).

There are three tables with the same columns:

segment_now is an external table whose data files are stored in $MASTER_DATA_DIRECTORY/gpperfmon/data. Current memory allocation data is stored in segment_now during the period between data collection from the gpperfmon agents and automatic commit to the segment_history table.
segment_tail is an external table whose data files are stored in $MASTER_DATA_DIRECTORY/gpperfmon/data. This is a transitional table for memory allocation data that has been cleared from segment_now but has not yet been committed to segment_history. It typically contains a few minutes worth of data. This table is for internal use only.
segment_history is a regular table that stores historical memory allocation metrics. It is partitioned into monthly partitions. Partitions are automatically added in two-month increments as needed.

A particular segment instance is identified by its hostname and dbid (the unique segment identifier as per the gp_segment_configuration system catalog table).

Column Type Description

Column	Type	Description
ctime	timestamp(0) without time zone	The time the row was created
dbid	int	The segment ID (`dbid` from `gp_segment_configuration`)
hostname	varchar(64)	The segment hostname
dynamic_memory_used	bigint	The amount of dynamic memory (in bytes) allocated to query processes running on this segment
dynamic_memory_available	bigint	The amount of additional dynamic memory (in bytes) that the segment can request before reaching the limit set by the currently active resource management scheme (resource groups or resource queues)

ctime

timestamp(0) without time zone

The time the row was created

dbid

int

The segment ID (dbid from gp_segment_configuration)

hostname

varchar(64)

The segment hostname

dynamic_memory_used

bigint

The amount of dynamic memory (in bytes) allocated to query processes running on this segment

dynamic_memory_available

bigint

The amount of additional dynamic memory (in bytes) that the segment can request before reaching the limit set by the currently active resource management scheme (resource groups or resource queues)

queries_*

socket_*