pg_backend_memory_contexts #
The view pg_backend_memory_contexts displays all
the memory contexts of the server process attached to the current session.
pg_backend_memory_contexts contains one row
for each memory context.
Table 55.5. pg_backend_memory_contexts Columns
Column Type Description |
|---|
Name of the memory context |
Identification information of the memory context. This field is truncated at 1024 bytes |
Type of the memory context |
The 1-based level of the context in the memory context hierarchy. The
level of a context also shows the position of that context in the
|
Array of transient numerical identifiers to describe the memory
context hierarchy. The first element is for
|
Total bytes allocated for this memory context |
Total number of blocks allocated for this memory context |
Free space in bytes |
Total number of free chunks |
Used space in bytes |
By default, the pg_backend_memory_contexts view can be
read only by superusers or roles with the privileges of the
pg_read_all_stats role.
Since memory contexts are created and destroyed during the running of a
query, the identifiers stored in the path column
can be unstable between multiple invocations of the view in the same query.
The example below demonstrates an effective usage of this column and
calculates the total number of bytes used by
CacheMemoryContext and all of its children:
WITH memory_contexts AS (
SELECT * FROM pg_backend_memory_contexts
)
SELECT sum(c1.total_bytes)
FROM memory_contexts c1, memory_contexts c2
WHERE c2.name = 'CacheMemoryContext'
AND c1.path[c2.level] = c2.path[c2.level];
The Common Table Expression is used
to ensure the context IDs in the path column
match between both evaluations of the view.