Merge pull request #2629 from wiredtiger/wt-2531

WT-2531: in-memory tables are wasting space in truncation

2 files changed, 16 insertions, 5 deletions

diff --git a/src/block/block_ckpt.c b/src/block/block_ckpt.c
index a0aadb43b93..a861a21876b 100644
--- a/src/block/block_ckpt.c
+++ b/src/block/block_ckpt.c
@@ -135,8 +135,11 @@ __wt_block_checkpoint_load(WT_SESSION_IMPL *session, WT_BLOCK *block,
 	 * that was done when the checkpoint was first written (re-writing the
 	 * checkpoint might possibly make it relevant here, but it's unlikely
 	 * enough I don't bother).
+	 *
+	 * If in-memory, we don't read or write the object, and the truncate
+	 * will unnecessarily allocate buffer space.
 	 */
-	if (!checkpoint) {
+	if (!checkpoint && !F_ISSET(S2C(session), WT_CONN_IN_MEMORY)) {
 		/*
 		 * The truncate might fail if there's a file mapping (if there's
 		 * an open checkpoint on the file), that's OK.
diff --git a/src/os_common/os_fs_inmemory.c b/src/os_common/os_fs_inmemory.c
index 5b9c849d225..218deb15d29 100644
--- a/src/os_common/os_fs_inmemory.c
+++ b/src/os_common/os_fs_inmemory.c
@@ -334,17 +334,25 @@ __im_handle_sync(WT_SESSION_IMPL *session, WT_FH *fh, bool block)
  *	POSIX ftruncate.
  */
 static int
-__im_handle_truncate(WT_SESSION_IMPL *session, WT_FH *fh, wt_off_t len)
+__im_handle_truncate(WT_SESSION_IMPL *session, WT_FH *fh, wt_off_t offset)
 {
 	WT_DECL_RET;
 	WT_IM *im;
+	size_t off;
 
 	im = S2C(session)->inmemory;
 	__wt_spin_lock(session, &im->lock);
 
-	WT_ERR(__wt_buf_grow(session, &fh->buf, (size_t)len));
-	memset((uint8_t *)
-	    fh->buf.mem + fh->buf.size, 0, fh->buf.memsize - fh->buf.size);
+	/*
+	 * Grow the buffer as necessary, clear any new space in the file,
+	 * and reset the file's data length.
+	 */
+	off = (size_t)offset;
+	WT_ERR(__wt_buf_grow(session, &fh->buf, off));
+	if (fh->buf.size < off)
+		memset((uint8_t *)
+		    fh->buf.data + fh->buf.size, 0, off - fh->buf.size);
+	fh->buf.size = off;
 
 err:	__wt_spin_unlock(session, &im->lock);
 	return (ret);