First version

Dockerfile

@@ -0,0 +1,15 @@
+ARG PG_MAJOR=15
+
+FROM postgres:$PG_MAJOR-bookworm
+
+RUN apt update
+
+RUN apt install -y postgresql-server-dev-$PG_MAJOR
+
+RUN apt install -y build-essential
+
+COPY . /build
+
+WORKDIR /build
+
+RUN make && make install

Makefile

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+EXTENSION = pg_lock_hash_info
+MODULES = pg_lock_hash_info
+DATA = pg_lock_hash_info--1.0.sql
+PG_CONFIG = pg_config
+
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)

pg_lock_hash_info--1.0.sql

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+CREATE FUNCTION pg_lock_hash_info()
+RETURNS TABLE (
+    hash_type CHAR,
+    directory INT,
+    bucket_hash INT,
+    entries INT,
+    free_slots INT
+) AS 'pg_lock_hash_info' LANGUAGE C STRICT;

pg_lock_hash_info.c

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+#include "postgres.h"
+#include "fmgr.h"
+#include "access/htup_details.h"
+#include "funcapi.h"
+#include "storage/lwlock.h"
+#include "storage/shmem.h"
+#include "utils/builtins.h"
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(pg_lock_hash_info);
+
+typedef struct {
+    int bucket_idx;
+    char hash_type;
+    int directory;
+    int entries;
+    int free_slots;
+} LockHashEntry;
+
+Datum
+pg_lock_hash_info(PG_FUNCTION_ARGS)
+{
+    FuncCallContext *funcctx;
+    LockHashEntry *entries;
+
+    if (SRF_IS_FIRSTCALL())
+    {
+        TupleDesc tupdesc;
+        MemoryContext oldcontext;
+
+        funcctx = SRF_FIRSTCALL_INIT();
+        oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+        tupdesc = CreateTemplateTupleDesc(5);
+        TupleDescInitEntry(tupdesc, (AttrNumber) 1, "hash_type", TEXTOID, -1, 0);
+        TupleDescInitEntry(tupdesc, (AttrNumber) 2, "directory", INT4OID, -1, 0);
+        TupleDescInitEntry(tupdesc, (AttrNumber) 3, "bucket_hash", INT4OID, -1, 0);
+        TupleDescInitEntry(tupdesc, (AttrNumber) 4, "entries", INT4OID, -1, 0);
+        TupleDescInitEntry(tupdesc, (AttrNumber) 5, "free_slots", INT4OID, -1, 0);
+        funcctx->tuple_desc = BlessTupleDesc(tupdesc);
+
+        /* Allocate space for results (this should fetch real data) */
+        entries = palloc(sizeof(LockHashEntry) * 10); /* Placeholder for real count */
+        funcctx->user_fctx = entries;
+        MemoryContextSwitchTo(oldcontext);
+    }
+
+    funcctx = SRF_PERCALL_SETUP();
+    entries = (LockHashEntry *) funcctx->user_fctx;
+
+    /* Placeholder loop to return mock data */
+    if (funcctx->call_cntr < 10)
+    {
+        Datum values[5];
+        bool nulls[5] = {false, false, false, false, false};
+        HeapTuple tuple;
+
+        values[0] = CharGetDatum(funcctx->call_cntr % 2 == 0 ? 'l' : 'p');
+        values[1] = Int32GetDatum(funcctx->call_cntr / 5);
+        values[2] = Int32GetDatum(funcctx->call_cntr);
+        values[3] = Int32GetDatum(5);  /* Fake number of entries */
+        values[4] = Int32GetDatum(10); /* Fake number of free slots */
+
+        tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
+        SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
+    }
+    else
+    {
+        SRF_RETURN_DONE(funcctx);
+    }
+}
+

pg_lock_hash_info.control

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+default_version = '1.0'
+comment = 'Expose lock and proclock hash bucket statistics'
+relocatable = false