Isolation Levels¶

Grafeo supports Snapshot Isolation by default.

Snapshot Isolation¶

Each transaction sees a consistent snapshot
Reads never block writes
Writes never block reads
Write conflicts detected at commit

Phenomena Prevented¶

Phenomenon	Prevented?
Dirty Read	Yes
Non-Repeatable Read	Yes
Phantom Read	Yes
Write Skew	Partially

Example¶

# Transaction 1
with db.session() as s1:
    s1.begin()
    # Sees snapshot at begin time

    # Transaction 2 commits changes
    with db.session() as s2:
        s2.execute("SET x = 100")

    # s1 still sees old value
    result = s1.execute("SELECT x")  # Old value
    s1.commit()

Conflict Detection¶

Write-write conflicts are detected:

# T1 and T2 both try to update same row
# Second to commit will fail with conflict error