Re: [PATCH 12/12] vinyl: allow to modify format of non-empty spaces

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Sat, Apr 07, 2018 at 04:38:09PM +0300, Vladimir Davydov wrote:
>  static int
>  vinyl_space_check_format(struct space *space, struct tuple_format *format)
>  {
> -	(void)format;
>  	struct vy_env *env = vy_env(space->engine);
> -	if (space->index_count == 0)
> +
> +	/*
> +	 * If this is local recovery, the space was checked before
> +	 * restart so there's nothing we need to do.
> +	 */
> +	if (env->status == VINYL_INITIAL_RECOVERY_LOCAL ||
> +	    env->status == VINYL_FINAL_RECOVERY_LOCAL)
>  		return 0;
> +
> +	if (space->index_count == 0)
> +		return 0; /* space is empty, nothing to do */
> +
> +	/*
> +	 * Iterate over all tuples stored in the given space and
> +	 * check each of them for conformity to the new format.
> +	 * Since read iterator may yield, we install an on_replace
> +	 * trigger to check tuples inserted after we started the
> +	 * iteration.
> +	 */
>  	struct vy_lsm *pk = vy_lsm(space->index[0]);
> -	if (env->status != VINYL_ONLINE)
> -		return 0;
> -	if (pk->stat.disk.count.rows == 0 && pk->stat.memory.count.rows == 0)
> -		return 0;
> -	diag_set(ClientError, ER_UNSUPPORTED, "Vinyl",
> -		 "changing format of a non-empty space");
> -	return -1;
> +
> +	struct tuple *key = vy_stmt_new_select(pk->env->key_format, NULL, 0);
> +	if (key == NULL)
> +		return -1;
> +
> +	struct trigger on_replace;
> +	struct vy_check_format_ctx ctx;
> +	ctx.format = format;
> +	ctx.is_failed = false;
> +	diag_create(&ctx.diag);
> +	trigger_create(&on_replace, vy_check_format_on_replace, &ctx, NULL);
> +	trigger_add(&space->on_replace, &on_replace);
> +
> +	struct vy_read_iterator itr;
> +	vy_read_iterator_open(&itr, pk, NULL, ITER_ALL, key,
> +			      &env->xm->p_global_read_view);
> +	int rc;
> +	struct tuple *tuple;
> +	while ((rc = vy_read_iterator_next(&itr, &tuple)) == 0) {
> +		if (tuple == NULL)
> +			break;

> +		if (ctx.is_failed) {
> +			diag_move(&ctx.diag, diag_get());
> +			rc = -1;
> +			break;
> +		}

This check should be before the EOF check (tuple == NULL), because even
in case read iterator returned NULL it may have yield, which might have
opened a time window for a concurrent fiber to insert a new tuple that
doesn't match the new format. Fixed on the branch. The incremental diff
is in the end of this email.

> +		rc = tuple_validate(format, tuple);
> +		if (rc != 0)
> +			break;
> +	}
> +	vy_read_iterator_close(&itr);
> +	diag_destroy(&ctx.diag);
> +	trigger_clear(&on_replace);
> +	tuple_unref(key);
> +	return rc;
>  }


diff --git a/src/box/vinyl.c b/src/box/vinyl.c
index c2769e6d..6bed09da 100644
--- a/src/box/vinyl.c
+++ b/src/box/vinyl.c
@@ -1104,13 +1104,13 @@ vinyl_space_check_format(struct space *space, struct tuple_format *format)
 	int rc;
 	struct tuple *tuple;
 	while ((rc = vy_read_iterator_next(&itr, &tuple)) == 0) {
-		if (tuple == NULL)
-			break;
 		if (ctx.is_failed) {
 			diag_move(&ctx.diag, diag_get());
 			rc = -1;
 			break;
 		}
+		if (tuple == NULL)
+			break;
 		rc = tuple_validate(format, tuple);
 		if (rc != 0)
 			break;