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1. Client reads A, B, C
2. Client reserves txid
3. Client writes A, B, C with lien to txid for some time (how long? see below)
4. Client writes T with (A', B', C') at txid
5. Client writes A' into A, B' into B, C' into C
6. Client deletes T

Consequences:

• A, B, C appear an extra time in the log with the liens.
• A', B', C' appear twice in the log.
• 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.
• Blind (unconditional) updates, deletes, and creates are no longer possible as the objects they operate on may have liens.
• Can only support creates using server-assigned object IDs if it is acceptable to burn object IDs when clients crash.

Server-Side Transactions (2PC)

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