This change introduces additional processes to manage snapshot uploading
for E2 snapshots:
## erigon snapshots upload
The `snapshots uploader` command starts a version of erigon customized
for uploading snapshot files to
a remote location.
It breaks the stage execution process after the senders stage and then
uses the snapshot stage to send
uploaded headers, bodies and (in the case of polygon) bor spans and
events to snapshot files. Because
this process avoids execution in run signifigantly faster than a
standard erigon configuration.
The uploader uses rclone to send seedable (100K or 500K blocks) to a
remote storage location specified
in the rclone config file.
The **uploader** is configured to minimize disk usage by doing the
following:
* It removes snapshots once they are loaded
* It aggressively prunes the database once entities are transferred to
snapshots
in addition to this it has the following performance related features:
* maximizes the workers allocated to snapshot processing to improve
throughput
* Can be started from scratch by downloading the latest snapshots from
the remote location to seed processing
## snapshots command
Is a stand alone command for managing remote snapshots it has the
following sub commands
* **cmp** - compare snapshots
* **copy** - copy snapshots
* **verify** - verify snapshots
* **manifest** - manage the manifest file in the root of remote snapshot
locations
* **torrent** - manage snapshot torrent files
"whitelisting" mechanism (list of files - stored in DB) - which
protecting us from downloading new files after upgrade/downgrade was
broken. And seems it became over-complicated with time.
I replacing it by 1 persistent flag inside downloader:
"prohibit_new_downloads.lock"
Erigon will turn downloader into this mode after
downloading/verification of first snapshots.
```
//Corner cases:
// - Erigon generated file X with hash H1. User upgraded Erigon. New version has preverified file X with hash H2. Must ignore H2 (don't send to Downloader)
// - Erigon "download once": means restart/upgrade/downgrade must not download files (and will be fast)
// - After "download once" - Erigon will produce and seed new files
```
------
`downloader --seedbox` is never "prohibit new downloads"
db must not use "Durable" and "SyncPeriod" in same time
txpool and downloader must be: Durable
nodedb: SafeNoSync+SyncPeriod
because txpool and downloader already can call sync when they need
(txpool after regular flush, downloader after piece download+validation
completion).
