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Updated Directories and Files (markdown)

Chris Lu 2019-08-05 11:48:45 -07:00
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Directories-and-Files.md

@ -72,49 +72,6 @@ For file renaming, it is just O(1) operations, with deleting the old metadata an
For directory renaming, it will be O(N) operations, with N as the number of files and folders underneath the to-be-renamed directory. This is because each of them will need to adjust the metadata. But still there are no change for the actual file content on volume servers. For directory renaming, it will be O(N) operations, with N as the number of files and folders underneath the to-be-renamed directory. This is because each of them will need to adjust the metadata. But still there are no change for the actual file content on volume servers.
### Comparing Storage Options
The Filer Store persists all file metadata and directory information.
| Filer Store Name | Lookup | number of entries in a folder | Scalability | Renaming | TTL | Note |
| ---------------- | -- | -- | -- | -- | -- | -- |
| memory | O(1) | limited by memory | Local, Fast | | | for testing only, no persistent storage |
| leveldb | O(logN)| unlimited | Local, Very Fast | | | Default, fairly scalable |
| leveldb2 | O(logN)| unlimited | Local, Very Fast, faster than leveldb | | | Similar to leveldb, part of the lookup key is 128bit MD5 instead of the long full file path |
| Redis | O(1) | limited | Local or Distributed, Fastest ||Yes| one directory's sub file names are stored in one key~value entry |
| Cassandra | O(logN)| unlimited | Local or Distributed, Very Fast||Yes| |
| MySql | O(logN)| unlimited | Local or Distributed, Fast |Atomic| | Easy to manage, export |
| Postgres | O(logN)| unlimited | Local or Distributed, Fast |Atomic| | Easy to manage, export |
| Etcd | O(logN)| ~10GB | Distributed, 10,000 writes/sec || | No SPOF. High Availability.|
#### Switching between different Stores
It is easy to switch between different filer stores.
For example:
```sh
# first save current filer meta data
$ weed shell
> fs.cd http://filerHost:filerPort/
> fs.meta.save
...
total 65 directories, 292 files
meta data for http://localhost:8888/ is saved to localhost-8888-20190417-005421.meta
> exit
# now switch to a new filer, and load the previously saved metadata
$ weed shell
> fs.meta.load localhost-8888-20190417-005421.meta
...
total 65 directories, 292 files
localhost-8888-20190417-005421.meta is loaded to http://localhost:8888/
```
### Extending Storage Options
For any new storage option, please implement the FilerStore interface. It should be fairly straight forward to implement. Welcome to contribute back.
### Use Cases ### Use Cases