Limits and unsupported features

Default resource limits

Limit	Default	Override
Materialized result	16 MiB	Database(result_buffer_limit=...)
Individual value	8 MiB	Database(maximum_value_size=...)
Executor workers	4	Database(worker_count=...)
Instance event queue	64 events	Database(event_queue_capacity=...)
C transport queue	64 KiB	pgm_instance_options.transport_queue_capacity
Logical archive channel	256 KiB	dump/restore options

A zero C or Python result-size option selects the embedded default; it does not mean unbounded memory.

Capacity rules

• One connection permits one in-flight request.
• Ordinary operations on one connection are serialized.
• Open transactions retain workers; simultaneously open transactions must not exceed the worker count.
• One host thread owns request or operation progress at a time.
• Logical dump and restore are serialized across the process.
• Event queue overflow is reported, not silently hidden.

Not currently supported

• PostgreSQL pipeline mode;
• COPY BOTH and replication protocol;
• shell-backed COPY ... PROGRAM and embedded system() / popen() calls;
• raw pgwire access from the public API;
• physical backup and restore;
• parallel pg_dump or pg_restore workers;
• arbitrary native extensions loaded from unbundled shared objects;
• PostgreSQL background-worker extensions under SDK ABI v1;
• C transaction callback helpers;
• source distributions for the Python package;
• a prebuilt shared C library as a first-release artifact;
• non-Linux or non-x86-64 public wheel policies;
• built-in encryption at rest for cluster directories or logical archives.

An unsupported capability must return PGM_STATUS_UNSUPPORTED in C or raise NotSupportedError in Python. PostGamma does not silently switch to a socket, subprocess, temporary archive file, or weaker SQL behavior.

The absence of shell execution is not a SQL sandbox. The initial role is a PostgreSQL superuser, and server-side file operations use the host process's filesystem permissions. See the security model.