735085 - prevent overlapping writes to same user/collection by different clients

Status: VERIFIED FIXED

(Cloud Services Graveyard :: Server: Sync, defect, P2)

Description

[Ryan Kelly [:rfkelly]]

Use a database-level lock to prevent this, per conversation with atoll

Comment 1

[Ryan Kelly [:rfkelly]]

This is the situation we're trying to avoid.  atoll, please correct if I misunderstand.

Client 1 uploads 100 records.  They get assigned timestamp1, and start being written to the database.  This is a big batch so it doesn't complete yet.

Client 2 uploads 1 record.  It gets assigned timestamp2 > timestamp1.  Because it's a small batch, they get written to the database before the above transaction completes.

Client 2's write completes,  it is told that X-Timestamp = timestamp2.

Client 1's write completes, it is told that X-Timestamp = timestamp1.

Problem: Client 2 will never retrieve the records uploaded by Client 1.

Potential Solution: lock something in the database that is unique to this userid/collectionid, so that the writes do not overlap.

Complication: This lock would need to be taken *before* assigning timestamps to the items, and *before* verifying that the write can proceed without conflict.

Comment 2

[Ryan Kelly [:rfkelly]]

This is done in sync1.5 with the new "session" objects, and will not be fixed for the going-away-real-soon-now sync1.1 codebase.

Comment 3

[James Bonacci [:jbonacci]]

OK.