Restore backup created by 0.6.4 with clickhouse-backup 1.0.0

[rodrigargar]

When restoring with clickhouse-backup 1.0.0 a backup created with a previous version of clickhouse-backup (0.6.4), I found a couple of issues:

1. Downloading the backup gives an is empty backup error, although the backup is not empty:

   $ clickhouse-backup download 2021-09-15-rnd-0.6.4-shard02
   2021/09/15 16:06:49 error '2021-09-15-rnd-0.6.4-shard02' is empty backup

@Slach gave me a workaround for this: allow empty backups in the configuration of clickhouse-backup.

general:
  allow_empty_backups: true

2. Restoring the schema tries to create the tables on the system database instead of the appropriate database.

In my case, the database rnd holds the events_local table and the events distributed table. When restoring the schema, clickhouse-backup tries to create the tables system.events_local and system.events (which already exists):

# LOG_LEVEL=debug clickhouse-backup restore --rm --schema 2021-09-15-rnd-0.6.4-shard02
...
2021/09/15 16:17:02 debug CREATE DATABASE IF NOT EXISTS `rnd`
2021/09/15 16:17:02 debug SELECT engine FROM system.databases WHERE name = 'rnd'
2021/09/15 16:17:02 debug DROP TABLE IF EXISTS `rnd`.`events_local`
2021/09/15 16:17:02 debug CREATE TABLE events_local
(
    `time` DateTime,
    `kind` UInt8,
    `host` String,
    `port` UInt16,
    `data` UInt32
)
ENGINE = ReplicatedMergeTree('/clickhouse/{cluster}/tables/{shard}/rnd.events_local', '{shard}_{replica}')
PARTITION BY toYear(time)
ORDER BY (time, kind)
SETTINGS index_granularity = 8192

2021/09/15 16:17:03 debug CREATE DATABASE IF NOT EXISTS `rnd`
2021/09/15 16:17:03 debug SELECT engine FROM system.databases WHERE name = 'rnd'
2021/09/15 16:17:03 debug DROP TABLE IF EXISTS `rnd`.`events`
2021/09/15 16:17:03 debug CREATE TABLE events
(
    `time` DateTime,
    `kind` UInt8,
    `host` String,
    `port` UInt16,
    `data` UInt32
)
ENGINE = Distributed('{cluster}', 'rnd', 'events_local', rand())

2021/09/15 16:17:03  warn can't create table 'rnd.events': code: 57, message: Table system.events already exists., will try again

Table events_local table is indeed created in the system database instead of the rnd database:

SHOW CREATE TABLE system.events_local

Row 1:
──────
statement: CREATE TABLE system.events_local
(
    `time` DateTime,
    `kind` UInt8,
    `host` String,
    `port` UInt16,
    `data` UInt32
)
ENGINE = ReplicatedMergeTree('/clickhouse/{cluster}/tables/{shard}/rnd.events_local', '{shard}_{replica}')
PARTITION BY toYear(time)
ORDER BY (time, kind)
SETTINGS index_granularity = 8192

---

Clickhouse-backup versions:

To create the backup:

$ clickhouse-backup --version
Version:         0.6.4
Git Commit:      4a0b3c040783232066f5b7ca4b2990d6ef50db19
Build Date:      2021-01-27

To restore the backup:

$ clickhouse-backup --version
Version:         1.0.0
Git Commit:      37f3bd78adec2aadc1de10f9323fe426a5e12dc4
Build Date:      2021-06-16