Restoring from GCS takes too long

Hello,

I'm trying to restore a postgres basebackup from Google Cloud Storage to Google Compute instance in the same zone.
I cannot figure out why, but `pghoard_restore` command needs ~106m to download and extract basebackup 18GB of size (48GB original size) while `gsutil` takes ~3 minutes only to download the same file.

During `pghoard_restore` avg network throughput is ~40MBit/s while `gsutil` turns it to `1.1GBit/s`.
What am I doing wrong? How can I tune the restore process somehow?

Pghoard config:
```json
{
"backup_location": "./metadata",
"backup_sites": {
"postgres-01": {
"active_backup_mode": "pg_receivexlog",
"basebackup_hour": 5,
"basebackup_interval_hours": 24,
"basebackup_minute": 40,
"pg_data_directory": "/var/lib/pgsql/9.5/data",
"nodes": [
{
"host": "postgres-01",
"user": "pghoard",
"password": "secret",
"port": 5432
}
],
"object_storage": {
"storage_type": "google",
"project_id": "postgres-dev",
"bucket_name": "test-pghoard"
}
}
}
}
```

Restore command:
```
pghoard_restore get-basebackup --config pghoard.json --recovery-target-time 2019-07-04T14:45:03+00:00 --restore-to-master --overwrite --target-dir /var/lib/pgsql/9.5/data/
```

Output:
```
Found 1 applicable basebackup

Basebackup Backup size Orig size Start time
---------------------------------------- ----------- ----------- --------------------
postgres-01/basebackup/2019-07-09_05-39_0 17687 MB 48779 MB 2019-07-09T05:41:38Z
metadata: {'backup-decision-time': '2019-07-09T05:39:45.442175+00:00', 'backup-reason': 'scheduled', 'normalized-backup-time': '2019-07-08T05:40:00+00:00', 'start-wal-segment': '000000040000C1120000009E', 'pg-version': '90504', 'compression-algorithm': 'snappy', 'compression-level': '0', 'original-file-size': '51148804096', 'host': 'postgres-01'}

Selecting 'postgres-01/basebackup/2019-07-09_05-39_0' for restore
2019-07-09 16:08:09,4699ChunkFetcher7687Thread-1 INFO Processing of 'postgres-01/basebackup/2019-07-09_05-39_0' completed successfully
Download progress: 100.00% (17687 / 17687 MiB)
Basebackup restoration complete.
You can start PostgreSQL by running pg_ctl -D /var/lib/pgsql/9.5/data/ start
On systemd based systems you can run systemctl start postgresql
On SYSV Init based systems you can run /etc/init.d/postgresql start
```