branches/innodb+: Refuse to buffer deletes if that could lead to B-tree

pages becoming empty.  Remove work-arounds for empty pages.  This fixes
Issue #82.

ibuf_get_volume_buffered(): Add the output parameter n_recs, for returning
the minimum number of records on the page.

ibuf_insert_low(): Refuse to buffer IBUF_OP_DELETE if the page could
become empty.

btr_page_get_father_node_ptr(): Remove the work-around for the page
being empty.

page_zip_dir_delete(): Revert to the version from branches/zip.
Always invoke page_zip_clear_rec().

btr/btr0btr.c

@@ -603,18 +603,7 @@ btr_page_get_father_node_ptr(
 	level = btr_page_get_level(btr_cur_get_page(cursor), mtr);
 
 	page = btr_cur_get_page(cursor);
-
-	if (UNIV_UNLIKELY(page_get_n_recs(page) == 0)) {
-		/* Empty pages can result from buffered delete operations.
-		The first record from the free list can be used to find the
-		father node. */
-		user_rec = page_header_get_ptr(page, PAGE_FREE);
-		/* TODO: make sure that empty pages are never recompressed. */
-		ut_a(user_rec);
-	} else {
 	user_rec = btr_cur_get_rec(cursor);
-	}
-
 	ut_a(page_rec_is_user_rec(user_rec));
 	tuple = dict_index_build_node_ptr(index, user_rec, 0, heap, level);
 

btr/btr0cur.c

@@ -658,9 +658,6 @@ btr_cur_search_to_nth_level(
 		page_mode = mode;
 	}
 
-	/* TO DO: if the page is empty, advance to the next page.
-	There may be a match on the first nonempty right sibling. */
-
 	page_cur_search_with_match(
 		block, index, tuple, page_mode, &up_match, &up_bytes,
 		&low_match, &low_bytes, page_cursor);

ibuf/ibuf0ibuf.c

@@ -2542,6 +2542,8 @@ ibuf_get_volume_buffered(
 				or BTR_MODIFY_TREE */
 	ulint		space,	/* in: space id */
 	ulint		page_no,/* in: page number of an index page */
+	ulint*		n_recs,	/* out: minimum number of records on the page
+				after the buffered changes have been applied */
 	mtr_t*		mtr)	/* in: mtr */
 {
 	ulint	volume;
@@ -2561,6 +2563,7 @@ ibuf_get_volume_buffered(
 	pcur */
 
 	volume = 0;
+	*n_recs = 0;
 
 	rec = btr_pcur_get_rec(pcur);
 	page = page_align(rec);
@@ -2657,6 +2660,20 @@ ibuf_get_volume_buffered(
 
 		volume += ibuf_rec_get_volume(rec);
 
+		switch (ibuf_rec_get_op_type(rec)) {
+		case IBUF_OP_INSERT:
+		case IBUF_OP_DELETE_MARK:
+			(*n_recs)++;
+			break;
+		case IBUF_OP_DELETE:
+			if (*n_recs > 0) {
+				(*n_recs)--;
+			}
+			break;
+		default:
+			ut_error;
+		}
+
 		rec = page_rec_get_next(rec);
 	}
 
@@ -2704,6 +2721,20 @@ ibuf_get_volume_buffered(
 
 		volume += ibuf_rec_get_volume(rec);
 
+		switch (ibuf_rec_get_op_type(rec)) {
+		case IBUF_OP_INSERT:
+		case IBUF_OP_DELETE_MARK:
+			(*n_recs)++;
+			break;
+		case IBUF_OP_DELETE:
+			if (*n_recs > 0) {
+				(*n_recs)--;
+			}
+			break;
+		default:
+			ut_error;
+		}
+
 		rec = page_rec_get_next(rec);
 	}
 }
@@ -2986,6 +3017,7 @@ ibuf_insert_low(
 	dtuple_t*	ibuf_entry;
 	mem_heap_t*	heap;
 	ulint		buffered;
+	ulint		min_n_recs;
 	rec_t*		ins_rec;
 	ibool		old_bit_value;
 	page_t*		bitmap_page;
@@ -3091,7 +3123,16 @@ ibuf_insert_low(
 
 	/* Find out the volume of already buffered inserts for the same index
 	page */
-	buffered = ibuf_get_volume_buffered(&pcur, space, page_no, &mtr);
+	buffered = ibuf_get_volume_buffered(&pcur, space, page_no,
+					    &min_n_recs, &mtr);
+
+	if (op == IBUF_OP_DELETE && min_n_recs == 0) {
+		/* The page could become empty after the record is
+		deleted.  Refuse to buffer the operation. */
+		err = DB_STRONG_FAIL;
+
+		goto function_exit;
+	}
 
 #ifdef UNIV_IBUF_COUNT_DEBUG
 	ut_a((buffered == 0) || ibuf_count_get(space, page_no));

page/page0zip.c

@@ -4116,29 +4116,9 @@ page_zip_dir_delete(
 	The "owned" and "deleted" flags will be cleared. */
 	mach_write_to_2(slot_free, page_offset(rec));
 
-	/* The compression algorithm expects info_bits and n_owned
-	to be 0 for deleted records. */
-	rec[-REC_N_NEW_EXTRA_BYTES] = 0; /* info_bits and n_owned */
-
-	if (!page_is_leaf(page)) {
+	if (!page_is_leaf(page) || !dict_index_is_clust(index)) {
 		ut_ad(!rec_offs_any_extern(offsets));
-		goto clear_rec;
-	}
-
-	if (!dict_index_is_clust(index)) {
-		ut_ad(!rec_offs_any_extern(offsets));
-
-		/* Do not clear the last record on a secondary index
-		leaf page, because that could break delete
-		buffering. */
-		if (!page_get_n_recs(page)) {
-#ifdef UNIV_ZIP_DEBUG
-			ut_a(page_zip_validate(page_zip, page));
-#endif /* UNIV_ZIP_DEBUG */
-			return;
-		}
-
-		goto clear_rec;
+		goto skip_blobs;
 	}
 
 	n_ext = rec_offs_n_extern(offsets);
@@ -4168,7 +4148,11 @@ page_zip_dir_delete(
 		memset(ext_end, 0, n_ext * BTR_EXTERN_FIELD_REF_SIZE);
 	}
 
-clear_rec:
+skip_blobs:
+	/* The compression algorithm expects info_bits and n_owned
+	to be 0 for deleted records. */
+	rec[-REC_N_NEW_EXTRA_BYTES] = 0; /* info_bits and n_owned */
+
 	page_zip_clear_rec(page_zip, rec, index, offsets);
 }