more work on exposing LFC stats

pgxn/neon/communicator/src/backend_interface.rs

@@ -252,6 +252,14 @@ pub unsafe extern "C" fn bcomm_cache_iterate_next(
     }
 }
 
+#[allow(clippy::missing_safety_doc)]
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn bcomm_cache_get_num_pages_used(
+    bs: &mut CommunicatorBackendStruct,
+) -> u64 {
+    bs.integrated_cache.get_num_buckets_in_use() as u64
+}
+
 impl<'t> CommunicatorBackendStruct<'t> {
     /// The slot must be free, or this panics.
     pub(crate) fn start_neon_io_request(&mut self, request_slot_idx: i32, request: &NeonIORequest) {

pgxn/neon/communicator/src/integrated_cache.rs

@@ -759,6 +759,10 @@ impl<'t> IntegratedCacheReadAccess<'t> {
             Some((key, _)) => GetBucketResult::Occupied(key.rel, key.block_number),
         }
     }
+
+    pub fn get_num_buckets_in_use(&self) -> usize {
+        self.block_map.get_num_buckets_in_use()
+    }
 }
 
 pub struct BackendCacheReadOp<'t> {

pgxn/neon/communicator_new.c

@@ -86,6 +86,10 @@ typedef struct CommunicatorShmemPerBackendData
 	 */
 	uint64		request_counter;
 
+	/* Counters, for metrics. */
+	uint64		cache_misses;
+	uint64		cache_hits;
+
 	/*
 	 * Normally, when reading or writing pages from shared buffer cache, the
 	 * worker process can operate directly on the shared buffer. But when
@@ -122,7 +126,8 @@ typedef struct CommunicatorShmemData
 
 static CommunicatorShmemData *communicator_shmem_ptr;
 
-#define MyIOCompletionLatch (&communicator_shmem_ptr->backends[MyProcNumber].io_completion_latch)
+static CommunicatorShmemPerBackendData *my_per_backend_data;
+#define MyIOCompletionLatch (&my_per_backend_data->io_completion_latch)
 
 #define MAX_INFLIGHT_ASYNC_REQUESTS 5
 
@@ -308,6 +313,8 @@ communicator_new_init(void)
 	if (MyBgworkerEntry && strcmp(MyBgworkerEntry->bgw_function_name, "communicator_new_bgworker_main") == 0)
 		return;
 
+	my_per_backend_data = &communicator_shmem_ptr->backends[MyProcNumber];
+
 	OwnLatch(MyIOCompletionLatch);
 
 	my_bs = rcommunicator_backend_init(cis, MyProcNumber);
@@ -753,6 +760,7 @@ retry:
 		}
 
 		pgBufferUsage.file_cache.hits += nblocks;
+		my_per_backend_data->cache_hits += nblocks;
 
 		return;
 	}
@@ -768,6 +776,7 @@ retry:
 	 * as a cache miss.
 	 */
 	pgBufferUsage.file_cache.misses += nblocks;
+	my_per_backend_data->cache_misses += nblocks;
 
 	wait_request_completion(request_idx, &result);
 	Assert(num_inflight_requests == 1);
@@ -1363,7 +1372,42 @@ communicator_new_approximate_working_set_size_seconds(time_t duration, bool rese
 LfcStatsEntry *
 communicator_new_get_lfc_stats(uint32 *num_entries)
 {
-	// TODO
-	*num_entries = 0;
-	return NULL;
+	LfcStatsEntry *entries;
+	int			n = 0;
+	uint64		cache_misses = 0;
+	uint64		cache_hits = 0;
+
+	for (int i = 0; i < MaxProcs; i++)
+	{
+		cache_misses += communicator_shmem_ptr->backends[i].cache_misses;
+		cache_hits += communicator_shmem_ptr->backends[i].cache_hits;
+	}
+
+#define NUM_ENTRIES 10
+	entries = palloc(sizeof(LfcStatsEntry) * NUM_ENTRIES);
+
+	entries[n++] = (LfcStatsEntry) {"file_cache_misses", false, cache_misses};
+	entries[n++] = (LfcStatsEntry) {"file_cache_hits", false, cache_hits };
+
+	entries[n++] = (LfcStatsEntry) {"file_cache_used_pages", false,
+									bcomm_cache_get_num_pages_used(my_bs) };
+
+	/* TODO: these stats are exposed by the legacy LFC implementation */
+#if 0
+	entries[n++] = (LfcStatsEntry) {"file_cache_used", lfc_ctl == NULL,
+									lfc_ctl ? lfc_ctl->used : 0 };
+	entries[n++] = (LfcStatsEntry) {"file_cache_writes", lfc_ctl == NULL,
+									lfc_ctl ? lfc_ctl->writes : 0 };
+	entries[n++] = (LfcStatsEntry) {"file_cache_size", lfc_ctl == NULL,
+									lfc_ctl ? lfc_ctl->size : 0 };
+	entries[n++] = (LfcStatsEntry) {"file_cache_evicted_pages", lfc_ctl == NULL,
+									lfc_ctl ? lfc_ctl->evicted_pages : 0 };
+	entries[n++] = (LfcStatsEntry) {"file_cache_limit", lfc_ctl == NULL,
+									lfc_ctl ? lfc_ctl->limit : 0 };
+#endif
+
+	Assert(n <= NUM_ENTRIES);
+
+	*num_entries = n;
+	return entries;
 }

pgxn/neon/neon.c

@@ -735,6 +735,7 @@ neon_get_lfc_stats(PG_FUNCTION_ARGS)
 		Datum		values[NUM_NEON_GET_STATS_COLS];
 		bool		nulls[NUM_NEON_GET_STATS_COLS];
 
+		nulls[0] = false;
 		values[0] = CStringGetTextDatum(entry->metric_name);
 		nulls[1] = entry->isnull;
 		values[1] = Int64GetDatum(entry->isnull ? 0 : entry->value);