segment_*
The segment_* tables contain memory allocation statistics for the SynxDB segment instances. This tracks the amount of memory consumed by all postgres 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 group-based or resource queue-based). See the SynxDB Administrator Guide for more information about resource management schemes.
There are three segment tables, all having the same columns:
segment_nowis an external table whose data files are stored in$MASTER_DATA_DIRECTORY/gpperfmon/data. Current memory allocation data is stored insegment_nowduring the period between data collection from thegpperfmonagents and automatic commitment to the segment_history table.segment_tailis an external table whose data files are stored in$MASTER_DATA_DIRECTORY/gpperfmon/data. This is a transitional table for memory allocation data that has been cleared fromsegment_nowbut has not yet been committed tosegment_history. It typically only contains a few minutes worth of data.segment_historyis a regular table that stores historical memory allocation metrics. It is pre-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 |
|---|---|---|
ctime | timestamp(0) (without time zone) | The time the row was created. |
dbid | int | The segment ID (dbid from gp_segment_configuration). |
hostname | charvar(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 group-based or resource queue-based). |
See also the views memory_info and dynamic_memory_info for aggregated memory allocation and utilization by host.