WT-3088 bug: WiredTiger can evict the tree's current eviction walk point (#3280)

WT-3088 bug: WiredTiger can evict the tree's current eviction walk point

5 files changed, 47 insertions, 42 deletions

diff --git a/src/btree/bt_debug.c b/src/btree/bt_debug.c
index a89eca230fd..d664da2ebd3 100644
--- a/src/btree/bt_debug.c
+++ b/src/btree/bt_debug.c
@@ -699,8 +699,6 @@ __debug_page_metadata(WT_DBG *ds, WT_REF *ref)
 		WT_RET(ds->f(ds, ", evict-lru"));
 	if (F_ISSET_ATOMIC(page, WT_PAGE_OVERFLOW_KEYS))
 		WT_RET(ds->f(ds, ", overflow-keys"));
-	if (F_ISSET_ATOMIC(page, WT_PAGE_SPLIT_BLOCK))
-		WT_RET(ds->f(ds, ", split-block"));
 	if (F_ISSET_ATOMIC(page, WT_PAGE_SPLIT_INSERT))
 		WT_RET(ds->f(ds, ", split-insert"));
 	if (F_ISSET_ATOMIC(page, WT_PAGE_UPDATE_IGNORE))
diff --git a/src/btree/bt_split.c b/src/btree/bt_split.c
index 7cfcd08f931..8122d242666 100644
--- a/src/btree/bt_split.c
+++ b/src/btree/bt_split.c
@@ -54,6 +54,16 @@ __split_oldest_gen(WT_SESSION_IMPL *session)
 }
 
 /*
+ * __wt_split_obsolete --
+ *	Check if it is safe to free / evict based on split generation.
+ */
+bool
+__wt_split_obsolete(WT_SESSION_IMPL *session, uint64_t split_gen)
+{
+	return (split_gen < __split_oldest_gen(session));
+}
+
+/*
  * __split_stash_add --
  *	Add a new entry into the session's split stash list.
  */
@@ -394,8 +404,8 @@ __split_ref_move(WT_SESSION_IMPL *session, WT_PAGE *from_home,
  *	Prepare a set of WT_REFs for a move.
  */
 static void
-__split_ref_step1(
-    WT_SESSION_IMPL *session, WT_PAGE_INDEX *pindex, bool skip_first)
+__split_ref_step1(WT_SESSION_IMPL *session,
+    WT_PAGE_INDEX *pindex, uint64_t split_gen, bool skip_first)
 {
 	WT_PAGE *child;
 	WT_REF *child_ref, *ref;
@@ -418,30 +428,25 @@ __split_ref_step1(
 		child = ref->page;
 
 		/*
-		 * Block eviction and splits in newly created pages.
+		 * Block eviction in newly created pages.
 		 *
 		 * Once the split is live, newly created internal pages might be
 		 * evicted and their WT_REF structures freed. If that happened
 		 * before all threads exit the index of the page that previously
 		 * "owned" the WT_REF, a thread might see a freed WT_REF. To
-		 * ensure that doesn't happen, the newly created page's modify
-		 * structure has a field with a transaction ID that's checked
-		 * before any internal page is evicted. Unfortunately, we don't
-		 * know the correct value until we update the original page's
-		 * index (we need a transaction ID from after that update), but
-		 * the act of updating the original page's index is what allows
-		 * the eviction to happen.
+		 * ensure that doesn't happen, the newly created page contains
+		 * the current split generation and can't be evicted until
+		 * all readers have left the old generation.
 		 *
-		 * Split blocking was because historic versions of the split
-		 * code didn't update the WT_REF.home field until after the
-		 * split was live, so the WT_REF.home fields being updated could
-		 * split again before the update, there's a race between splits
-		 * as to which would update them first. The current code updates
-		 * the WT_REF.home fields before going live (in this function),
-		 * this shouldn't be an issue, but for now splits remain turned
-		 * off.
+		 * Historic, we also blocked splits in newly created pages
+		 * because we didn't update the WT_REF.home field until after
+		 * the split was live, so the WT_REF.home fields being updated
+		 * could split again before the update, there's a race between
+		 * splits as to which would update them first. The current code
+		 * updates the WT_REF.home fields before going live (in this
+		 * function), this isn't an issue.
 		 */
-		F_SET_ATOMIC(child, WT_PAGE_SPLIT_BLOCK);
+		child->pg_intl_split_gen = split_gen;
 
 		/*
 		 * We use a page flag to prevent the child from splitting from
@@ -473,7 +478,6 @@ __split_ref_step2(
     WT_SESSION_IMPL *session, WT_PAGE_INDEX *pindex, bool skip_first)
 {
 	WT_DECL_RET;
-	WT_PAGE *child;
 	WT_REF *ref;
 	uint32_t i;
 
@@ -503,14 +507,9 @@ __split_ref_step2(
 			continue;
 		WT_ERR(ret);
 
-		child = ref->page;
-
-		/* The child can now be evicted or split. */
-		F_CLR_ATOMIC(child, WT_PAGE_SPLIT_BLOCK);
-
 #ifdef HAVE_DIAGNOSTIC
 		WT_WITH_PAGE_INDEX(session,
-		    __split_verify_intl_key_order(session, child));
+		    __split_verify_intl_key_order(session, ref->page));
 #endif
 
 		WT_ERR(__wt_hazard_clear(session, ref));
@@ -653,8 +652,12 @@ __split_root(WT_SESSION_IMPL *session, WT_PAGE *root)
 	/* Start making real changes to the tree, errors are fatal. */
 	complete = WT_ERR_PANIC;
 
+	/* Get a generation for this split, mark the root page. */
+	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
+	root->pg_intl_split_gen = split_gen;
+
 	/* Prepare the WT_REFs for the move. */
-	__split_ref_step1(session, alloc_index, false);
+	__split_ref_step1(session, alloc_index, split_gen, false);
 
 	/*
 	 * Confirm the root page's index hasn't moved, then update it, which
@@ -686,7 +689,6 @@ __split_root(WT_SESSION_IMPL *session, WT_PAGE *root)
 	 * fails, we don't roll back that change, because threads may already
 	 * be using the new index.
 	 */
-	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
 	size = sizeof(WT_PAGE_INDEX) + pindex->entries * sizeof(WT_REF *);
 	WT_TRET(__split_safe_free(session, split_gen, false, pindex, size));
 	root_decr += size;
@@ -838,6 +840,10 @@ __split_parent(WT_SESSION_IMPL *session, WT_REF *ref, WT_REF **ref_new,
 	/* Start making real changes to the tree, errors are fatal. */
 	complete = WT_ERR_PANIC;
 
+	/* Get a generation for this split, mark the parent page. */
+	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
+	parent->pg_intl_split_gen = split_gen;
+
 	/*
 	 * Confirm the parent page's index hasn't moved then update it, which
 	 * makes the split visible to threads descending the tree.
@@ -908,7 +914,6 @@ __split_parent(WT_SESSION_IMPL *session, WT_REF *ref, WT_REF **ref_new,
 	 *
 	 * Acquire a new split generation.
 	 */
-	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
 	for (i = 0, deleted_refs = scr->mem; i < deleted_entries; ++i) {
 		next_ref = pindex->index[deleted_refs[i]];
 		WT_ASSERT(session, next_ref->state == WT_REF_SPLIT);
@@ -1160,8 +1165,12 @@ __split_internal(WT_SESSION_IMPL *session, WT_PAGE *parent, WT_PAGE *page)
 	/* Start making real changes to the tree, errors are fatal. */
 	complete = WT_ERR_PANIC;
 
+	/* Get a generation for this split, mark the page. */
+	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
+	page->pg_intl_split_gen = split_gen;
+
 	/* Prepare the WT_REFs for the move. */
-	__split_ref_step1(session, alloc_index, true);
+	__split_ref_step1(session, alloc_index, split_gen, true);
 
 	/* Split into the parent. */
 	WT_ERR(__split_parent(session, page_ref, alloc_index->index,
@@ -1207,7 +1216,6 @@ __split_internal(WT_SESSION_IMPL *session, WT_PAGE *parent, WT_PAGE *page)
 	 * back that change, because threads may already be using the new parent
 	 * page.
 	 */
-	split_gen = __wt_atomic_addv64(&S2C(session)->split_gen, 1);
 	size = sizeof(WT_PAGE_INDEX) + pindex->entries * sizeof(WT_REF *);
 	WT_TRET(__split_safe_free(session, split_gen, false, pindex, size));
 	page_decr += size;
@@ -1284,10 +1292,6 @@ __split_internal_lock(WT_SESSION_IMPL *session, WT_REF *ref, bool trylock,
 	for (;;) {
 		parent = ref->home;
 
-		/* Skip pages that aren't ready to split. */
-		if (F_ISSET_ATOMIC(parent, WT_PAGE_SPLIT_BLOCK))
-			return (EBUSY);
-
 		if (trylock)
 			WT_RET(__wt_try_writelock(session, &parent->page_lock));
 		else
diff --git a/src/include/btmem.h b/src/include/btmem.h
index 43c1a309d52..39ca223aebf 100644
--- a/src/include/btmem.h
+++ b/src/include/btmem.h
@@ -483,6 +483,7 @@ struct __wt_page {
 		 */
 		struct {
 			WT_REF	*parent_ref;	/* Parent reference */
+			uint64_t split_gen;	/* Generation of last split */
 
 			struct __wt_page_index {
 				uint32_t entries;
@@ -492,6 +493,8 @@ struct __wt_page {
 		} intl;
 #undef	pg_intl_parent_ref
 #define	pg_intl_parent_ref		u.intl.parent_ref
+#undef	pg_intl_split_gen
+#define	pg_intl_split_gen		u.intl.split_gen
 
 	/*
 	 * Macros to copy/set the index because the name is obscured to ensure
@@ -593,9 +596,8 @@ struct __wt_page {
 #define	WT_PAGE_DISK_MAPPED	0x04	/* Disk image in mapped memory */
 #define	WT_PAGE_EVICT_LRU	0x08	/* Page is on the LRU queue */
 #define	WT_PAGE_OVERFLOW_KEYS	0x10	/* Page has overflow keys */
-#define	WT_PAGE_SPLIT_BLOCK	0x20	/* Split blocking eviction and splits */
-#define	WT_PAGE_SPLIT_INSERT	0x40	/* A leaf page was split for append */
-#define	WT_PAGE_UPDATE_IGNORE	0x80	/* Ignore updates on page discard */
+#define	WT_PAGE_SPLIT_INSERT	0x20	/* A leaf page was split for append */
+#define	WT_PAGE_UPDATE_IGNORE	0x40	/* Ignore updates on page discard */
 	uint8_t flags_atomic;		/* Atomic flags, use F_*_ATOMIC */
 
 	uint8_t unused[2];		/* Unused padding */
diff --git a/src/include/btree.i b/src/include/btree.i
index 378d93dd2ee..315efa86fa6 100644
--- a/src/include/btree.i
+++ b/src/include/btree.i
@@ -1348,8 +1348,8 @@ __wt_page_can_evict(
 	 * discards its WT_REF array, and a thread traversing the original
 	 * parent page index might see a freed WT_REF.
 	 */
-	if (WT_PAGE_IS_INTERNAL(page) &&
-	    F_ISSET_ATOMIC(page, WT_PAGE_SPLIT_BLOCK))
+	if (WT_PAGE_IS_INTERNAL(page) && !__wt_split_obsolete(
+	    session, page->pg_intl_split_gen))
 		return (false);
 
 	/*
diff --git a/src/include/extern.h b/src/include/extern.h
index 863d2a02861..836a7cb1ae6 100644
--- a/src/include/extern.h
+++ b/src/include/extern.h
@@ -160,6 +160,7 @@ __wt_page_in_func(WT_SESSION_IMPL *session, WT_REF *ref, uint32_t flags
 extern int __wt_bt_rebalance(WT_SESSION_IMPL *session, const char *cfg[]) WT_GCC_FUNC_DECL_ATTRIBUTE((warn_unused_result)) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
 extern int __wt_kv_return(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt, WT_UPDATE *upd) WT_GCC_FUNC_DECL_ATTRIBUTE((warn_unused_result)) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
 extern int __wt_bt_salvage(WT_SESSION_IMPL *session, WT_CKPT *ckptbase, const char *cfg[]) WT_GCC_FUNC_DECL_ATTRIBUTE((warn_unused_result)) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
+extern bool __wt_split_obsolete(WT_SESSION_IMPL *session, uint64_t split_gen) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
 extern void __wt_split_stash_discard(WT_SESSION_IMPL *session) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
 extern void __wt_split_stash_discard_all( WT_SESSION_IMPL *session_safe, WT_SESSION_IMPL *session) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));
 extern int __wt_multi_to_ref(WT_SESSION_IMPL *session, WT_PAGE *page, WT_MULTI *multi, WT_REF **refp, size_t *incrp, bool closing) WT_GCC_FUNC_DECL_ATTRIBUTE((warn_unused_result)) WT_GCC_FUNC_DECL_ATTRIBUTE((visibility("hidden")));