Sybase 12.4.2 manual Hold cursors span transactions, 297

CHAPTER 8 Transactions and Versioning

•If a user's read transaction commits before a concurrent write transaction does, and that user begins a new read transaction, the version remains the same.

•If a read transaction commits after a concurrent write transaction does, any new transaction, whether read-only or read/write, uses a new version.

Figure 8-4 on page 296 is an example of the first instance. Both of User 2's transactions use the same version as User 1's transaction began with, because that is the latest committed version of the data.

Figure 8-5 shows what happens in the second instance. This time, User 2's first read transaction (Tr1) commits after User 1's write transaction. When User 2's second transaction (Tr2) begins, it uses a new version that reflects the committed data from User 1.

Figure 8-5: Effect of read transaction committing

Hold cursors span transactions

The only exception to the rule that transactions always use the latest committed version is in transactions that use hold cursors. Hold cursors are treated differently because they can span transactions. See “Cursors in transactions” for details.

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