Speed up checkpoints by doing a better job of skipping pages that can't contain changes that need to be included.

Before the checkpoint pass, we have written every dirty leaf page at read-committed isolation.  So the only pages that checkpoint has to write are internal pages, or leaf pages that were dirtied after the "write leaves" phase but before the checkpoint transaction started.  Now that we separate out the allocation of a transaction ID from setting up a snapshot, we can distinguish between update transactions and the transaction we're using for the checkpoint.

refs #954, #963, #1001

1 files changed, 5 insertions, 25 deletions

diff --git a/src/btree/bt_sync.c b/src/btree/bt_sync.c
index 84e5261310e..d8114a6019a 100644
--- a/src/btree/bt_sync.c
+++ b/src/btree/bt_sync.c
@@ -23,7 +23,7 @@ __sync_file(WT_SESSION_IMPL *session, int syncop)
 	WT_TXN *txn;
 	uint64_t internal_bytes, leaf_bytes;
 	uint64_t internal_pages, leaf_pages;
-	uint32_t checkpoint_gen, flags;
+	uint32_t flags;
 
 	btree = S2BT(session);
 	walk = NULL;
@@ -70,7 +70,6 @@ __sync_file(WT_SESSION_IMPL *session, int syncop)
 		 * eviction to complete.
 		 */
 		btree->checkpointing = 1;
-		checkpoint_gen = ++btree->checkpoint_gen;
 
 		if (!F_ISSET(btree, WT_BTREE_NO_EVICTION)) {
 			WT_ERR(__wt_evict_file_exclusive_on(session));
@@ -88,19 +87,12 @@ __sync_file(WT_SESSION_IMPL *session, int syncop)
 			 * Write dirty pages, unless we can be sure they only
 			 * became dirty after the checkpoint started.
 			 *
-			 * We can skip pages if:
+			 * We can skip dirty pages if:
 			 * (1) they are leaf pages;
-			 * (2) the global checkpoint generation has been
-			 *     incremented (otherwise we skip writing the
-			 *     metadata when first creating tables);
-			 * (3) the page's checkpoint generation is equal to
-			 *     the current checkpoint generation, so it has
-			 *     already been written since this checkpoint
-			 *     started; and
-			 * (4) there is a snapshot transaction active (which
+			 * (2) there is a snapshot transaction active (which
 			 *     is the case in ordinary application checkpoints
 			 *     but not all internal cases); and
-			 * (5) any updates skipped by reconciliation were
+			 * (3) the first dirty update on the page is
 			 *     sufficiently recent that the checkpoint
 			 *     transaction would skip them.
 			 */
@@ -108,10 +100,8 @@ __sync_file(WT_SESSION_IMPL *session, int syncop)
 			mod = page->modify;
 			if (__wt_page_is_modified(page) &&
 			    (WT_PAGE_IS_INTERNAL(page) ||
-			    checkpoint_gen == 0 ||
-			    mod->checkpoint_gen < checkpoint_gen ||
 			    !F_ISSET(txn, TXN_HAS_SNAPSHOT) ||
-			    TXNID_LE(mod->rec_skipped_txn, txn->snap_max))) {
+			    TXNID_LE(mod->first_dirty_txn, txn->snap_max))) {
 				if (WT_PAGE_IS_INTERNAL(page)) {
 					internal_bytes +=
 					    page->memory_footprint;
@@ -122,17 +112,7 @@ __sync_file(WT_SESSION_IMPL *session, int syncop)
 				}
 				WT_ERR(__wt_rec_write(session, walk, NULL, 0));
 			}
-
-			/*
-			 * Set the checkpoint generation, even if we didn't
-			 * write the page.  If it becomes dirty and is selected
-			 * for eviction, it can't be written until this
-			 * checkpoint completes.
-			 */
-			if (page->modify != NULL)
-				page->modify->checkpoint_gen = checkpoint_gen;
 		}
-		WT_ASSERT(session, checkpoint_gen == btree->checkpoint_gen);
 		break;
 	WT_ILLEGAL_VALUE_ERR(session);
 	}