Nov 4, 2017

Four Isolation levels of the SQL standard

The SQL standard defines four Isolation levels:

  1. READ_UNCOMMITTED
  2. READ_COMMITTED
  3. REPEATABLE_READ
  4. SERIALIZABLE
All but the SERIALIZABLE level are subject to data anomalies (phenomena) that might occur according to the following pattern:
Isolation LevelDirty readNon-repeatable readPhantom read
READ_UNCOMMITTEDallowedallowedallowed
READ_COMMITTEDpreventedallowedallowed
REPEATABLE_READpreventedpreventedallowed
SERIALIZABLEpreventedpreventedprevented