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Client-Side Transactions

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Assuming initially object ID 1 contains A, 2 contains B, 3 contains C.

1. Client reserves txid
2. Client writes A, B, C with lien to txid for some time (how long? see below)
3. Client writes T with (A', B', C') at txidwrites placeholder T with object IDs (1, 2, 3)
4. Client adds masks to objects 1, 2, 3 which all point to T
5. Client updates T with (write A' at 1 over version V1, write B' at 2 over version V2, write C' at 3 over version V3)
6. Client writes A' into A1, B' into B2, C' into C3
7. Client deletes T

Consequences

• 1:A, 2:B, 3:C appear an extra time in the log with the liens(when they are masked).
• A', B', C' appear twice an extra time in the log (in T).
• Client clocks must be synchronized The objects in a transaction should have lien expiry times larger than the time it takes to recover a server: this could be a relatively long time. If the client crashes (instead of a server), the objects involved must stay locked until the lien expires.and/or other clients must always wait some amount of time before aborting a transaction
• Blind (unconditional) updates, deletes, and creates modifications are no longer possible as the objects they operate on may have liensbe masked.
• Can only support creates using server-assigned object IDs if it is acceptable to burn object IDs when clients crash.
• It'd be hard to do this safely if we need to consider access control. (We don't with namespaces.)

Server-Side Transactions (2PC)

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