Use bump context for TID bitmaps stored by vacuum

Vacuum does not pfree individual entries, and only frees the entire
storage space when finished with it. This allows using a bump context,
eliminating the chunk header in each leaf allocation. Most leaf
allocations will be 16 to 32 bytes, so that's a significant savings.
TidStoreCreateLocal gets a boolean parameter to indicate that the
created store is insert-only.

This requires a separate tree context for iteration, since we free
the iteration state after iteration completes.

Discussion: https://postgr.es/m/CANWCAZac%3DpBePg3rhX8nXkUuaLoiAJJLtmnCfZsPEAS4EtJ%3Dkg%40mail.gmail.com
Discussion: https://postgr.es/m/CANWCAZZQFfxvzO8yZHFWtQV+Z2gAMv1ku16Vu7KWmb5kZQyd1w@mail.gmail.com

src/backend/access/common/tidstore.c

@@ -120,7 +120,7 @@ static void tidstore_iter_extract_tids(TidStoreIter *iter, BlockNumber blkno,
  * by TidStoreMemoryUsage().
  */
 TidStore *
-TidStoreCreateLocal(size_t max_bytes)
+TidStoreCreateLocal(size_t max_bytes, bool insert_only)
 {
 	TidStore   *ts;
 	size_t		initBlockSize = ALLOCSET_DEFAULT_INITSIZE;
@@ -138,11 +138,22 @@ TidStoreCreateLocal(size_t max_bytes)
 		maxBlockSize = ALLOCSET_DEFAULT_INITSIZE;
 
 	/* Create a memory context for the TID storage */
-	ts->rt_context = AllocSetContextCreate(CurrentMemoryContext,
+	if (insert_only)
+	{
+		ts->rt_context = BumpContextCreate(CurrentMemoryContext,
 										   "TID storage",
 										   minContextSize,
 										   initBlockSize,
 										   maxBlockSize);
+	}
+	else
+	{
+		ts->rt_context = AllocSetContextCreate(CurrentMemoryContext,
+											   "TID storage",
+											   minContextSize,
+											   initBlockSize,
+											   maxBlockSize);
+	}
 
 	ts->tree.local = local_ts_create(ts->rt_context);
 

src/backend/access/heap/vacuumlazy.c

@@ -2874,7 +2874,7 @@ dead_items_alloc(LVRelState *vacrel, int nworkers)
 	dead_items_info->num_items = 0;
 	vacrel->dead_items_info = dead_items_info;
 
-	vacrel->dead_items = TidStoreCreateLocal(dead_items_info->max_bytes);
+	vacrel->dead_items = TidStoreCreateLocal(dead_items_info->max_bytes, true);
 }
 
 /*
@@ -2910,7 +2910,7 @@ dead_items_reset(LVRelState *vacrel)
 
 	/* Recreate the tidstore with the same max_bytes limitation */
 	TidStoreDestroy(dead_items);
-	vacrel->dead_items = TidStoreCreateLocal(vacrel->dead_items_info->max_bytes);
+	vacrel->dead_items = TidStoreCreateLocal(vacrel->dead_items_info->max_bytes, true);
 
 	/* Reset the counter */
 	vacrel->dead_items_info->num_items = 0;

src/include/access/tidstore.h

@@ -29,7 +29,7 @@ typedef struct TidStoreIterResult
 	OffsetNumber *offsets;
 } TidStoreIterResult;
 
-extern TidStore *TidStoreCreateLocal(size_t max_bytes);
+extern TidStore *TidStoreCreateLocal(size_t max_bytes, bool insert_only);
 extern TidStore *TidStoreCreateShared(size_t max_bytes, int tranche_id);
 extern TidStore *TidStoreAttach(dsa_handle area_handle, dsa_pointer handle);
 extern void TidStoreDetach(TidStore *ts);

src/include/lib/radixtree.h

@@ -691,6 +691,7 @@ struct RT_RADIX_TREE
 	/* leaf_context is used only for single-value leaves */
 	MemoryContextData *leaf_context;
 #endif
+	MemoryContextData *iter_context;
 };
 
 /*
@@ -1796,6 +1797,14 @@ RT_CREATE(MemoryContext ctx)
 	tree = (RT_RADIX_TREE *) palloc0(sizeof(RT_RADIX_TREE));
 	tree->context = ctx;
 
+	/*
+	 * Separate context for iteration in case the tree context doesn't support
+	 * pfree
+	 */
+	tree->iter_context = AllocSetContextCreate(ctx,
+											   RT_STR(RT_PREFIX) "radix_tree iter context",
+											   ALLOCSET_SMALL_SIZES);
+
 #ifdef RT_SHMEM
 	tree->dsa = dsa;
 	dp = dsa_allocate0(dsa, sizeof(RT_RADIX_TREE_CONTROL));
@@ -2038,7 +2047,7 @@ RT_BEGIN_ITERATE(RT_RADIX_TREE * tree)
 	RT_ITER    *iter;
 	RT_CHILD_PTR root;
 
-	iter = (RT_ITER *) MemoryContextAllocZero(tree->context,
+	iter = (RT_ITER *) MemoryContextAllocZero(tree->iter_context,
 											  sizeof(RT_ITER));
 	iter->tree = tree;
 

src/test/modules/test_tidstore/test_tidstore.c

@@ -116,7 +116,8 @@ test_create(PG_FUNCTION_ARGS)
 		dsa_pin_mapping(TidStoreGetDSA(tidstore));
 	}
 	else
-		tidstore = TidStoreCreateLocal(tidstore_max_size);
+		/* VACUUM uses insert only, so we test the other option. */
+		tidstore = TidStoreCreateLocal(tidstore_max_size, false);
 
 	tidstore_empty_size = TidStoreMemoryUsage(tidstore);