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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.
### 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