WT-3486 Discard obsolete updates as part of re-instantiating updates based on the lookaside table. (#3561)

2 files changed, 29 insertions, 6 deletions

diff --git a/src/btree/bt_read.c b/src/btree/bt_read.c
index 004a6b6c943..49b12b2d4e9 100644
--- a/src/btree/bt_read.c
+++ b/src/btree/bt_read.c
@@ -81,12 +81,22 @@ err:	/*
  */
 static int
 __col_instantiate(WT_SESSION_IMPL *session,
-    uint64_t recno, WT_REF *ref, WT_CURSOR_BTREE *cbt, WT_UPDATE *upd)
+    uint64_t recno, WT_REF *ref, WT_CURSOR_BTREE *cbt, WT_UPDATE *updlist)
 {
+	WT_PAGE *page;
+	WT_UPDATE *upd;
+
+	page = ref->page;
+
+	/* Discard any of the updates we don't need. */
+	if (updlist->next != NULL &&
+	    (upd = __wt_update_obsolete_check(session, page, updlist)) != NULL)
+		__wt_update_obsolete_free(session, page, upd);
+
 	/* Search the page and add updates. */
 	WT_RET(__wt_col_search(session, recno, ref, cbt));
 	WT_RET(__wt_col_modify(
-	    session, cbt, recno, NULL, upd, upd->type, false));
+	    session, cbt, recno, NULL, updlist, updlist->type, false));
 	return (0);
 }
 
@@ -96,11 +106,22 @@ __col_instantiate(WT_SESSION_IMPL *session,
  */
 static int
 __row_instantiate(WT_SESSION_IMPL *session,
-    WT_ITEM *key, WT_REF *ref, WT_CURSOR_BTREE *cbt, WT_UPDATE *upd)
+    WT_ITEM *key, WT_REF *ref, WT_CURSOR_BTREE *cbt, WT_UPDATE *updlist)
 {
+	WT_PAGE *page;
+	WT_UPDATE *upd;
+
+	page = ref->page;
+
+	/* Discard any of the updates we don't need. */
+	if (updlist->next != NULL &&
+	    (upd = __wt_update_obsolete_check(session, page, updlist)) != NULL)
+		__wt_update_obsolete_free(session, page, upd);
+
 	/* Search the page and add updates. */
 	WT_RET(__wt_row_search(session, key, ref, cbt, true));
-	WT_RET(__wt_row_modify(session, cbt, key, NULL, upd, upd->type, false));
+	WT_RET(__wt_row_modify(
+	    session, cbt, key, NULL, updlist, updlist->type, false));
 	return (0);
 }
 
diff --git a/src/btree/row_modify.c b/src/btree/row_modify.c
index a57a9c17edb..6e610b86376 100644
--- a/src/btree/row_modify.c
+++ b/src/btree/row_modify.c
@@ -330,9 +330,11 @@ __wt_update_obsolete_check(
 
 	/*
 	 * If the list is long, don't retry checks on this page until the
-	 * transaction state has moved forwards.
+	 * transaction state has moved forwards. This function is used to
+	 * trim update lists independently of the page state, ensure there
+	 * is a modify structure.
 	 */
-	if (count > 20)
+	if (count > 20 && page->modify != NULL)
 		page->modify->obsolete_check_txn =
 		    S2C(session)->txn_global.last_running;