[venus] Failed to export snapshot file

[cloudxin]

Checklist

• [X] This is not a security-related bug/issue. If it is, please follow please follow the security policy.
• [X] This is not a question or a support request. If you have any lotus related questions, please ask in the venus forum.
• [X] This is not a new feature request. If it is, please file a feature request instead.
• [X] This is not an enhancement request. If it is, please file a improvement suggestion instead.
• [X] I have searched on the issue tracker and the venus forum, and there is no existing related issue or discussion.
• [X] I am running the latest release, or the most recent RC(release canadiate) for the upcoming release or the dev branch(master), or have an issue updating to any of these.
• [ ] I did not make any code changes to venus.

Venus component

• [X] venus daemon - chain sync
• [ ] venus auth - authentication
• [ ] venus gateway - chain service gateway
• [ ] venus miner - mining and block production
• [ ] venus sealer/worker - sealing
• [ ] venus sealer - proving(WindowPoSt)
• [ ] venus market - storage deal
• [ ] venus market - retrieval deal
• [ ] venus market - data transfer
• [ ] venus light-weight client
• [ ] venus JSON-RPC API
• [ ] venus messager - message management (mpool)
• [ ] Other

Venus Version

venus version
{
	"Version": "1.2.4+git.135232873.dirty"
}

Describe the Bug

./venus chain export --recent-stateroots=920 --skip-old-msgs snapshot.car

Logging Information

Exporting snapshot files takes too long and takes up a lot of memory. 128G systems have memory overflow problems.

Repo Steps

1. Run '...'
2. Do '...'
3. See error '...' ...