Transaction Isolation Levels (cont)
A PostgreSQL tx consists of a sequence of SQL statements:
BEGIN S1; S2; ... Sn; COMMIT;
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Isolation levels affect view of DB provided to each Si:
- in read committed ...
- each Si sees snapshot of DB at start of Si
- in repeatable read and serializable ...
- each Si sees snapshot of DB at start of tx
- serializable checks for extra conditions
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