Add pg_stat_statements_nsp extension for DSM-based query statistics

contrib/pg_stat_statements_nsp/.gitignore

@@ -0,0 +1,6 @@
+# Generated by regression tests
+/results/
+/regression.diffs
+/regression.out
+/tmp_check/
+/log/

contrib/pg_stat_statements_nsp/Makefile

@@ -0,0 +1,23 @@
+# contrib/pg_stat_statements_nsp/Makefile
+
+MODULE_big = pg_stat_statements_nsp
+OBJS = \
+	$(WIN32RES) \
+	pg_stat_statements_nsp.o
+
+EXTENSION = pg_stat_statements_nsp
+DATA = pg_stat_statements_nsp--1.0.sql
+PGFILEDESC = "pg_stat_statements_nsp - execution statistics without shared_preload_libraries"
+
+REGRESS = pg_stat_statements_nsp
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/pg_stat_statements_nsp
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

contrib/pg_stat_statements_nsp/README.md

@@ -0,0 +1,107 @@
+# pg_stat_statements_nsp
+
+A query statistics extension that works **without** requiring `shared_preload_libraries`.
+
+## Overview
+
+This extension demonstrates how to use the DSM (Dynamic Shared Memory) Registry,
+introduced in PostgreSQL 17, to create shared data structures that persist across
+sessions without needing to be loaded at server startup.
+
+Unlike the standard `pg_stat_statements`, this extension can be loaded dynamically
+via the `LOAD` command or `session_preload_libraries`, making it ideal for:
+
+- Cloud environments where modifying `shared_preload_libraries` requires a restart
+- Development and testing scenarios
+- Situations where you want to enable query tracking without server downtime
+
+## Key Features
+
+- **No server restart required**: Load via `LOAD 'pg_stat_statements_nsp'`
+- **Shared statistics**: Statistics are shared across all sessions once initialized
+- **Similar API**: Provides a familiar interface similar to `pg_stat_statements`
+
+## Limitations
+
+Compared to the full `pg_stat_statements`:
+
+- Statistics do **not** persist across server restarts (no disk storage)
+- Fixed maximum number of tracked statements (1000)
+- Simplified statistics (no planning stats, WAL stats, etc.)
+- Query text is not stored (only query IDs are tracked)
+- No GUC parameters for configuration
+
+## Installation
+
+1. Build and install:
+   ```bash
+   cd contrib/pg_stat_statements_nsp
+   make
+   make install
+   ```
+
+2. Create the extension in your database:
+   ```sql
+   CREATE EXTENSION pg_stat_statements_nsp;
+   ```
+
+## Usage
+
+1. Enable query ID computation and load the module:
+   ```sql
+   SET compute_query_id = on;
+   LOAD 'pg_stat_statements_nsp';
+   ```
+
+2. Run some queries to collect statistics:
+   ```sql
+   SELECT 1;
+   SELECT * FROM pg_class LIMIT 10;
+   ```
+
+3. View the collected statistics:
+   ```sql
+   SELECT * FROM pg_stat_statements_nsp;
+   ```
+
+4. Reset statistics:
+   ```sql
+   SELECT pg_stat_statements_nsp_reset();
+   ```
+
+## Output Columns
+
+| Column | Type | Description |
+|--------|------|-------------|
+| userid | oid | User OID who executed the query |
+| dbid | oid | Database OID where query was executed |
+| queryid | bigint | Query identifier (hash) |
+| calls | bigint | Number of times executed |
+| total_time | double precision | Total execution time in milliseconds |
+| min_time | double precision | Minimum execution time |
+| max_time | double precision | Maximum execution time |
+| mean_time | double precision | Mean execution time |
+| rows | bigint | Total rows retrieved or affected |
+
+## Technical Details
+
+This extension uses:
+
+- **DSM Registry** (`GetNamedDSMSegment`, `GetNamedDSHash`): For lazy allocation
+  of shared memory without requiring `shared_preload_libraries`
+- **dshash**: A concurrent hash table that supports dynamic resizing in DSM
+- **Executor hooks**: To track query execution (works without preload)
+
+## Requirements
+
+- PostgreSQL 17 or later (for DSM Registry `GetNamedDSHash` support)
+- `compute_query_id` must be enabled (either `on` or `auto`)
+
+## See Also
+
+- `pg_stat_statements` - The full-featured query statistics extension
+- DSM Registry documentation in PostgreSQL source
+
+## License
+
+PostgreSQL License

contrib/pg_stat_statements_nsp/expected/pg_stat_statements_nsp.out

@@ -0,0 +1,84 @@
+-- Test pg_stat_statements_nsp extension
+-- This extension works without shared_preload_libraries
+-- First, ensure compute_query_id is enabled
+SET compute_query_id = on;
+-- Load the extension module (this simulates loading via LOAD command)
+LOAD 'pg_stat_statements_nsp';
+-- Create the extension (installs functions and views)
+CREATE EXTENSION pg_stat_statements_nsp;
+-- Reset any existing statistics
+SELECT pg_stat_statements_nsp_reset();
+ pg_stat_statements_nsp_reset 
+------------------------------
+
+(1 row)
+
+-- Run some test queries
+SELECT 1 AS simple_select;
+ simple_select 
+---------------
+             1
+(1 row)
+
+SELECT 1 + 1 AS addition;
+ addition 
+----------
+        2
+(1 row)
+
+SELECT generate_series(1, 5);
+ generate_series 
+-----------------
+               1
+               2
+               3
+               4
+               5
+(5 rows)
+
+-- Create a test table and run some queries on it
+CREATE TABLE test_nsp (id int, val text);
+INSERT INTO test_nsp VALUES (1, 'one'), (2, 'two'), (3, 'three');
+SELECT * FROM test_nsp WHERE id = 1;
+ id | val 
+----+-----
+  1 | one
+(1 row)
+
+UPDATE test_nsp SET val = 'ONE' WHERE id = 1;
+DELETE FROM test_nsp WHERE id = 3;
+-- Check that we have recorded statistics
+-- Note: We check for non-zero calls rather than exact counts
+-- because query IDs might vary across runs
+SELECT
+    calls > 0 AS has_calls,
+    total_time >= 0 AS has_time,
+    rows >= 0 AS has_rows
+FROM pg_stat_statements_nsp
+WHERE dbid = (SELECT oid FROM pg_database WHERE datname = current_database())
+LIMIT 5;
+ has_calls | has_time | has_rows 
+-----------+----------+----------
+ t         | t        | t
+ t         | t        | t
+ t         | t        | t
+ t         | t        | t
+ t         | t        | t
+(5 rows)
+
+-- Check the view works
+SELECT count(*) > 0 AS has_entries FROM pg_stat_statements_nsp;
+ has_entries 
+-------------
+ t
+(1 row)
+
+-- Clean up
+DROP TABLE test_nsp;
+SELECT pg_stat_statements_nsp_reset();
+ pg_stat_statements_nsp_reset 
+------------------------------
+
+(1 row)
+
+DROP EXTENSION pg_stat_statements_nsp;

contrib/pg_stat_statements_nsp/pg_stat_statements_nsp--1.0.sql

@@ -0,0 +1,43 @@
+/* contrib/pg_stat_statements_nsp/pg_stat_statements_nsp--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_stat_statements_nsp" to load this file. \quit
+
+-- Register the function to retrieve statistics
+CREATE FUNCTION pg_stat_statements_nsp(
+    OUT userid oid,
+    OUT dbid oid,
+    OUT queryid bigint,
+    OUT calls bigint,
+    OUT total_time double precision,
+    OUT min_time double precision,
+    OUT max_time double precision,
+    OUT rows bigint
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_statements_nsp'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+-- Register the function to reset statistics
+CREATE FUNCTION pg_stat_statements_nsp_reset()
+RETURNS void
+AS 'MODULE_PATHNAME', 'pg_stat_statements_nsp_reset'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+-- Create a view for convenient access
+CREATE VIEW pg_stat_statements_nsp AS
+SELECT
+    s.userid,
+    s.dbid,
+    s.queryid,
+    s.calls,
+    s.total_time,
+    s.min_time,
+    s.max_time,
+    CASE WHEN s.calls > 0 THEN s.total_time / s.calls ELSE 0 END AS mean_time,
+    s.rows
+FROM pg_stat_statements_nsp() s;
+
+-- Grant access to pg_read_all_stats role (like pg_stat_statements does)
+GRANT SELECT ON pg_stat_statements_nsp TO pg_read_all_stats;
+GRANT EXECUTE ON FUNCTION pg_stat_statements_nsp() TO pg_read_all_stats;