[JAMES-3433] Specify blobStore read performance expectation

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Done
• Affects Version/s: master
• Fix Version/s: 3.6.0
• Component/s: Blob
• Assignee: Unassigned
• Reporter: Benoit Tellier
• Created: 22/Oct/20 01:43
• Updated: 04/Nov/20 02:19
• Resolved: 26/Oct/20 02:58

Description

1. 1. Why

https://github.com/apache/james-project/blob/master/src/adr/0014-blobstore-storage-policies.md

James exposes a simple BlobStore API for storing raw data. However such raw data often vary in size and access patterns.

As an example:

• Mailbox message headers are expected to be small and frequently accessed
• Mailbox message body are expected to have sizes ranging from small to big but are unfrequently accessed
• Mailbox attachments body are expected to have sizes ranging from small to big but are unfrequently accessed
• DeletedMessageVault message headers are expected to be small and unfrequently accessed

Caching frequently accessed data for which low latencies is expected is worth it.

Caching infrequently, non-latency-sensitive data like bodies, attachment is a waste of resources. We should stop doing it.

1. 1. Definition of done

Write an integration test demonstrating that small mail bodies do not end up in the blobStore cache.

1. 1. How

Upon reads (bytes or stream) the reader specifies which storage policy he whishes to use.

Upon LOW_COST reads the CachedBlobStore only queries the back-end, and don't query the cache, nor populate it. Today behavior happens when using HIGH_PERFORMANCE (query the cache and populates it if missing).

Use HIGH_PERFORMANCE read level when reading headers, LOW_COST otherwize.