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https://issues.apache.org/jira/browse/JAMES-2921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16950758#comment-16950758
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Benoit Tellier commented on JAMES-2921:
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It's design was "I want to rely on a new solution (object storage) while
accessing my old blobs (in cassandra)"
Which turns out to be pretty different from "I would like to get the best of
both world" statement.
But given than migration is partial (no live/batch migration, only union) the
union blob store makes little sens to me.
> Improve blob store usage
> ------------------------
>
> Key: JAMES-2921
> URL: https://issues.apache.org/jira/browse/JAMES-2921
> Project: James Server
> Issue Type: Wish
> Components: Blob
> Reporter: Benoit Tellier
> Priority: Major
> Attachments: adr-0003-blobstore-storage-policies.md,
> adr-0003-blobstore-storage-policies.md,
> adr-0004-objectstorage-blobid-list.md, adr-0004-objectstorage-blobid-list.md
>
>
> Please find attached the two technical decisions being proposed.
> These needs performance feedback before being adopted.
> h2. Proposal: Add storage policies for BlobStore
> Introduce StoragePolicies at the level of the BlobStore API.
> The proposed policies includes:
> - SizeBasedStoragePolicy: The blob underlying storage medium will be chosen
> depending of its size.
> - LowCostStoragePolicy: The blob is expected to be saved in low cost
> storage. Access is expected to be unfrequent.
> - PerformantStoragePolicy: The blob is expected to be saved in performant
> storage. Access is expected to be unfrequent.
> The UnionBlobStore will be reworked to choose between Cassandra and
> ObjectStorage implementations depending on the policies.
> DeletedMessageVault, BlobExport & MailRepository will rely on
> LowCostStoragePolicy. Other BlobStore users will rely on
> SizeBasedStoragePolicy.
> h2. Proposal: persist BlobIds for avoiding persisting several time the same
> blobs within ObjectStorage
> Rely on a StoredBlobIdsList API to know which blob is persisted or not in
> object storage. Provide a Cassandra implementation of it. Located in blob-api
> for convenience, this in not a top level API. It is intended to be used by
> some blobStore implementations (here only ObjectStorage).
> - When saving a blob with precomputed blobId, we can check the existance of
> the blob in storage, avoiding possibly the expensive "save".
> - When saving a blob too big to precompute its blobId, once the blob had
> been stream using a temporary random blobId, copy operation can be avoided
> and the temporary blob could be directly removed.
> Cassandra is faster doing "write every time" rather than "read before write"
> so we should not use the storedblob projection for it
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