Index: subversion/include/private/svn_wc_private.h
===================================================================
--- subversion/include/private/svn_wc_private.h	(revision 1292379)
+++ subversion/include/private/svn_wc_private.h	(working copy)
@@ -263,6 +263,15 @@
                                      apr_pool_t *result_pool,
                                      apr_pool_t *scratch_pool);
 
+/* Close the DB for LOCAL_ABSPATH.  Perform temporary allocations in
+   SCRATCH_POOL.
+   
+   Wraps svn_wc__db_drop_root(). */
+svn_error_t *
+svn_wc__close_db(const char *external_abspath,
+                 svn_wc_context_t *wc_ctx,
+                 apr_pool_t *scratch_pool);
+
 /** Set @a *tree_conflict to a newly allocated @c
  * svn_wc_conflict_description_t structure describing the tree
  * conflict state of @a victim_abspath, or to @c NULL if @a victim_abspath
Index: subversion/libsvn_client/externals.c
===================================================================
--- subversion/libsvn_client/externals.c	(revision 1292379)
+++ subversion/libsvn_client/externals.c	(working copy)
@@ -299,6 +299,9 @@
                                       external_peg_rev,
                                       external_rev,
                                       pool));
+    /* Issue #4123: We don't need to keep the newly checked out external's
+       DB open. */
+    SVN_ERR(svn_wc__close_db(local_abspath, ctx->wc_ctx, pool));
   }
 
   return SVN_NO_ERROR;
Index: subversion/libsvn_wc/externals.c
===================================================================
--- subversion/libsvn_wc/externals.c	(revision 1292379)
+++ subversion/libsvn_wc/externals.c	(working copy)
@@ -1363,6 +1363,16 @@
     }
 }
 
+svn_error_t *
+svn_wc__close_db(const char *external_abspath,
+                 svn_wc_context_t *wc_ctx,
+                 apr_pool_t *scratch_pool)
+{
+  SVN_ERR(svn_wc__db_drop_root(wc_ctx->db, external_abspath,
+                               scratch_pool));
+  return SVN_NO_ERROR;
+}
+
 /* Return the scheme of @a uri in @a scheme allocated from @a pool.
    If @a uri does not appear to be a valid URI, then @a scheme will
    not be updated.  */