Isolation Level Performance:

1. Lock Duration:

Read Uncommitted: No locks (fastest)

Read Committed: Short locks (released immediately after read)

Repeatable Read: Long locks (held until transaction ends)

Serializable: Range locks (held until transaction ends, locks entire range)

Impact: Longer locks = more waiting = slower throughput

2. Lock Contention:

Read Committed: Low contention (locks released quickly)

Repeatable Read: Medium contention (locks held longer)

Serializable: High contention (range locks block inserts/updates/deletes)

Example: 1000 concurrent transactions reading same account

- Read Committed: All execute concurrently (short locks)

- Repeatable Read: Execute sequentially (long locks, wait for each other)

- Serializable: Execute sequentially (range locks, highest wait time)

3. Deadlock Frequency:

Read Committed: Low deadlock risk (short locks, less overlap)

Repeatable Read: Medium deadlock risk (long locks, more overlap)

Serializable: High deadlock risk (range locks, most overlap)

Example: Two transactions updating different accounts

- Read Committed: Low deadlock risk (locks released quickly)

- Serializable: High deadlock risk (range locks may overlap)

4. Throughput Comparison:

Test: 1000 concurrent transactions, same query

- Read Uncommitted: 1000 TPS (no locks)

- Read Committed: 900 TPS (10% slower, short locks)

- Repeatable Read: 500 TPS (50% slower, long locks)

- Serializable: 100 TPS (90% slower, range locks + deadlocks)

5. Transaction Duration:

Read Committed: Fast (< 10ms for simple query)

Repeatable Read: Slower (10-50ms, waiting for locks)

Serializable: Slowest (50-500ms, waiting for range locks + deadlock retries)

6. Optimization Strategies:

Use Read Committed for most transactions:

- 99% of applications do not need stronger isolation

- High throughput (900+ TPS)

- Low deadlock risk

Use Repeatable Read for reports:

- Need consistent snapshot (same query returns same results)

- Can tolerate slower performance (reports run off-peak)