Sybase 12.4.2 manual Transactions use committed data, 295

CHAPTER 8 Transactions and Versioning

Figure 8-3: Concurrent insertions to different tables

Data definition operations on a single table lock out all other readers and writers from that table. See “Locks for DDL operations” for details.

Transactions use committed data

Committed data results when a write transaction commits. Every transaction uses the latest committed version of the database as of the time the transaction begins. It uses that version until the transaction commits.

The time a transaction begins is called its Start Timestamp. The start timestamp can be any time before the transaction's first read. Any insertions and deletions the transaction makes are reflected in the snapshot. Thus, for the user executing a transaction, the image in the snapshot changes whenever that transaction writes data to the table, and then reads it again. For all other users, the image remains static until their transaction commits.

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