I recently noticed that the cost for ListBucket calls was increasing for an
application that was using Litestream. After investigating it seemed that the
bucket had retained the entire history of data, while Litestream was
continually logging that it was deleting the same data:
```
2022-10-30T12:00:27Z (s3): wal segmented deleted before 0792d3393bf79ced/00000233: n=1428
<snip>
2022-10-30T13:00:24Z (s3): wal segmented deleted before 0792d3393bf79ced/00000233: n=1428
```
This is occuring because the DeleteObjects call is a batch item, that returns
the individual object deletion errors in the response[1]. The S3 replica client
discards the response, and only handles errors in the original API call. I had
a misconfigured IAM policy that meant all deletes were failing, but this never
actually bubbled up as a real error.
To fix this, I added a check for the response body to handle any errors the
operation might have encountered. Because this may include a large number of
errors (in this case 1428 of them), the output is summarized to avoid an overly
large error message. When items are not found, they will not return an error[2]
- they will still be marked as deleted, so this change should be in-line with
the original intentions of this code.
1: https://docs.aws.amazon.com/AmazonS3/latest/API/API_DeleteObjects.html#API_DeleteObjects_Example_2
2: https://docs.aws.amazon.com/AmazonS3/latest/API/API_DeleteObjects.html
Previously, Litestream would avoid closing the SQLite3 connection
in order to ensure that the WAL file was not cleaned up by the
database if it was the last connection. This commit changes the
behavior by introducing a file control call to perform the same
action. This allows us to close the database file normally in all
cases.
Previously, a bug was introduced that added a `LIST` operation
on every replica sync which significantly increased the cost of
running Litestream against S3. This changes the behavior to only
issue the `LIST` operation when the generation has changed.
