[PATCH 3/3] wal: create empty xlog on shutdown

[Konstantin Osipov]

* Vladimir Davydov <vdavydov.dev at gmail.com> [18/06/15 23:28]:
>  recovery_finalize(struct recovery *r)
>  {
>  	recovery_close_log(r);
> -
> -	/*
> -	 * Check if next xlog exists. If it's true this xlog is
> -	 * corrupted and we should rename it (to avoid getting
> -	 * problem on the next xlog write with the same name).
> -	 * Possible reasons are:
> -	 *  - last xlog has corrupted rows
> -	 *  - last xlog has corrupted header
> -	 *  - last xlog has zero size
> -	 */
> -	char *name = xdir_format_filename(&r->wal_dir,
> -					  vclock_sum(&r->vclock),
> -					  NONE);
> -	if (access(name, F_OK) == 0) {
> -		say_info("rename corrupted xlog %s", name);
> -		char to[PATH_MAX];
> -		snprintf(to, sizeof(to), "%s.corrupted", name);
> -		if (rename(name, to) != 0) {
> -			tnt_raise(SystemError,
> -				  "%s: can't rename corrupted xlog",
> -				  name);
> -		}
> -	}

I agree this hunk should be moved to wal.c, but I don't understand
why it has to be done in wal thread.

Please make it obvious by leaving only the necessary parts in
wal_init_f and adding a comment.

> --- a/src/box/wal.c
> +++ b/src/box/wal.c
> @@ -310,6 +310,39 @@ wal_thread_start()
>  	cpipe_set_max_input(&wal_thread.wal_pipe, IOV_MAX);
>  }
>  
> +static int
> +wal_init_f(struct cbus_call_msg *msg)

Please add a formal comment for this function.

>  /**
>   * Initialize WAL writer.
>   *
> @@ -332,6 +365,11 @@ wal_init(enum wal_mode wal_mode, const char *wal_dirname,
>  	if (xdir_scan(&writer->wal_dir))
>  		return -1;
>  
> +	struct cbus_call_msg msg;
> +	if (cbus_call(&wal_thread.wal_pipe, &wal_thread.tx_pipe, &msg,
> +		      wal_init_f, NULL, TIMEOUT_INFINITY) != 0)
> +		return -1;
> +

> +	/*
> +	 * Create a new empty WAL on shutdown so that we don't have
> +	 * to rescan the last WAL to find the instance vclock.
> +	 */
> +	if (writer->wal_mode != WAL_NONE &&
> +	    xdir_create_xlog(&writer->wal_dir, &writer->current_wal,
> +			     &writer->vclock) == 0)
> +		xlog_close(&writer->current_wal, false);

In case there is an existing empty xlog file, this function fails
to create a new one and returns an error which you ignore.

Please handle this case nicely and avoid trying to create a new
xlog file if it is not necessary.

>  

-- 
Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov