import chain and import snapshot are ambiguous

[travisperson]

Both the --import-chain and --import-snapshot do almost the exact same thing but from their descriptions I have no idea which I should use or how to properly use lotus chain export for either. We need to document their use cases, and preferably remove one and replace it with a boolean, as at the moment import snapshot does the exact same thing as import chain except it doesn't validate anything.

[TippyFlitsUK]

Hi @travisperson

This looks like a reminder. Should we close it or keep it open?

[travisperson]

I think we should keep it open, I think most people coming to the project would still have a hard time understanding what each of the flags do.

It would be good to take some time and think about the two flag descriptions and see if there is a better way to communicate their purpose. This can also be done by adding a description to the daemon command that provides some more details about importing and then references the chain export command.

   --import-chain value      on first run, load chain from given file or url and validate
   --import-snapshot value   import chain state from a given chain export file or url

I think some additional details on the export command would also help, as well as some thought into the flag descriptions.

Eg specify the number of recent state roots to include in the export is miss-leading. This is not a number of TipSet to export, unless a null round is considered a TipSet (I would not define them as such). We actually are taking the height of the provided TipSet and walking back the number of epochs that --recent-stateroots specifies by simply subtracting that number. So if the export tipset epoch height is 525,000 and a user provides --recent-stateroots=2000, that further back tipset will be ~523,000 and will contain <= 2000 stateroots.

lotus/chain/store/snapshot.go

Lines 124 to 137 in 5416ce5

	if b.Height == 0 || b.Height > ts.Height()-inclRecentRoots {
	if walked.Visit(b.ParentStateRoot) {
	cids, err := recurseLinks(ctx, cs.stateBlockstore, walked, b.ParentStateRoot, []cid.Cid{b.ParentStateRoot})
	if err != nil {
	return xerrors.Errorf("recursing genesis state failed: %w", err)
	}
	out = append(out, cids...)
	}
	if !skipMsgReceipts && walked.Visit(b.ParentMessageReceipts) {
	out = append(out, b.ParentMessageReceipts)
	}
	}

[github-actions]

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