feat(mito): Add WriteCache struct and write SSTs to write cache

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR implements a skeleton for the WriteCache that serves as a write-through cache for object stores.

WriteCache

The WriteCache has a local store to cache files.

pub struct WriteCache {
    /// Local file cache.
    file_cache: FileCacheRef,
    /// Object store manager.
    object_store_manager: ObjectStoreManagerRef,
}

The WriteCache has a write_and_upload_sst() method to write files to the cache (a local store) and upload them to object stores.

pub(crate) async fn write_and_upload_sst(
    &self,
    request: SstUploadRequest,
    write_opts: &WriteOptions,
) -> Result<Option<SstInfo>>

Upload can be sync or async. We will implement the sync version first.

The recover() method will recover the underlying file cache.

pub async fn recover(&self) -> Result<()>;

The AccessLayer hides the details of writing SSTs to the write cache.

impl AccessLayer {
    pub(crate) async fn write_sst(
        &self,
        request: SstWriteRequest,
        write_opts: &WriteOptions,
    ) -> Result<Option<SstInfo>> {
        // ...
    }
}

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

• mito: Write cache for remote object store #2965

[codecov]

Codecov Report

Attention: 38 lines in your changes are missing coverage. Please review.

Comparison is base (f1a4750) 85.68% compared to head (962a9d1) 85.13%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2999      +/-   ##
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- Coverage   85.68%   85.13%   -0.56%     
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  Files         806      806              
  Lines      131511   131563      +52     
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- Hits       112689   112003     -686     
- Misses      18822    19560     +738     

[killme2008]

LGTM

[evenyag]

After some experiments, I plan to simplify the implementation of the write-through cache and upload files to object stores synchronously. Then we can remove UploadPart related components. I'll get back soon.

[evenyag]

I refactored the AccessLayer and WriteCache:

• 0278513 refactors the AccessLayer to hide the details of writing SST files.
• 9f03e67 writes the SST to the write cache, though it doesn't go through the local file cache.