Oracle DB Transactions — Fuzzy Read

Non-repeatable or fuzzy read: Transaction T1 reads a data item. Another transaction T2 then modifies or deletes that data item and commits. If T1 then attempts to reread the data item, it receives a modified value or discovers that the data item has been deleted.

r1[x]…w2[x]…c2…r1[x]…c1

💡 How to read the shorthand notations? w means write, r means read, number(1 or 2) indicates transaction id, c means commit and a means abort/rollback

Fuzzy read occurs in “READ COMMITTED” isolation level in Oracle

Fuzzy read does not occur in “SERIALIZABLE” isolation level in Oracle

💡Serializable isolation level in Oracle is actually a “Snapshot Isolation”

Transaction 1

Transaction 2

Transaction 2