Transaction Isolation

Transaction isolation in Geode ensures that concurrent transactions execute correctly without interference, maintaining data consistency and integrity. 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Not recommended for production use. <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Begin transaction with read uncommitted (not recommended) BEGIN TRANSACTION ISOLATION LEVEL READ UNCOMMITTED; -- Can see uncommitted changes from other transactions MATCH (p:Person) RETURN p.name, p.balance; COMMIT; </code></pre></div>Phenomena Prevented: None Performance: Highest Use Case: Approximate queries where consistency is not critical <h4 id="read-committed-default" class="position-relative d-flex align-items-center group"> Read Committed (Default) <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="read-committed-default" aria-haspopup="dialog" aria-label="Share link: Read Committed (Default)"> Share link </button> </h4>Prevents dirty reads by only reading committed data. Default isolation level in Geode. <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Begin transaction with read committed (default) BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED; -- Only sees committed data, but may see different values on repeated reads MATCH (p:Person {id: $person_id}) RETURN p.balance; -- If another transaction commits a balance update, next read may see different value MATCH (p:Person {id: $person_id}) RETURN p.balance; -- May return different balance COMMIT; </code></pre></div>Phenomena Prevented: Dirty reads Performance: High Use Case: Most applications where consistency within a transaction is needed <h4 id="repeatable-read" class="position-relative d-flex align-items-center group"> Repeatable Read <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="repeatable-read" aria-haspopup="dialog" aria-label="Share link: Repeatable Read"> Share link </button> </h4>Prevents dirty reads and non-repeatable reads. Same data returns same values throughout transaction. <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Begin transaction with repeatable read BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ; -- First read MATCH (p:Person {id: $person_id}) RETURN p.balance; -- Guaranteed to return the same balance even if another transaction commits changes MATCH (p:Person {id: $person_id}) RETURN p.balance; -- Same value as first read COMMIT; </code></pre></div>Phenomena Prevented: Dirty reads, non-repeatable reads Performance: Medium Use Case: Reports and analytics requiring consistent snapshots <h4 id="snapshot-isolation-recommended" class="position-relative d-flex align-items-center group"> Snapshot Isolation (Recommended) <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="snapshot-isolation-recommended" aria-haspopup="dialog" aria-label="Share link: Snapshot Isolation (Recommended)"> Share link </button> </h4>Geode’s enhanced isolation level using multi-version concurrency control (MVCC). Provides excellent balance of consistency and performance. <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Begin transaction with snapshot isolation (recommended) BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; -- Sees a consistent snapshot of the database as of transaction start MATCH (p:Person)-[:WORKS_AT]->(c:Company) WHERE c.industry = 'technology' RETURN count(p) AS tech_workers; -- Another transaction inserts new Person nodes -- This query still sees the original snapshot MATCH (p:Person)-[:WORKS_AT]->(c:Company) WHERE c.industry = 'technology' RETURN count(p) AS tech_workers; -- Same count as before COMMIT; </code></pre></div>Phenomena Prevented: Dirty reads, non-repeatable reads, phantom reads Performance: High (uses MVCC, no read locks) Use Case: Most enterprise applications, recommended default <h4 id="serializable" class="position-relative d-flex align-items-center group"> Serializable <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="serializable" aria-haspopup="dialog" aria-label="Share link: Serializable"> Share link </button> </h4>Strictest isolation level, guarantees transactions execute as if run serially. <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Begin transaction with serializable isolation BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; -- Check inventory level MATCH (p:Product {sku: $sku}) WHERE p.inventory > $quantity RETURN p.inventory; -- Reserve inventory MATCH (p:Product {sku: $sku}) SET p.inventory = p.inventory - $quantity; -- No other transaction can modify this product concurrently -- Prevents write skew anomalies COMMIT; </code></pre></div>Phenomena Prevented: All (dirty reads, non-repeatable reads, phantom reads, write skew) Performance: Lower (uses pessimistic locking) Use Case: Financial transactions, inventory management, critical operations <h3 id="concurrency-control" class="position-relative d-flex align-items-center group"> Concurrency Control <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="concurrency-control" aria-haspopup="dialog" aria-label="Share link: Concurrency Control"> Share link </button> </h3>Geode uses different concurrency control mechanisms depending on isolation level: <h4 id="multi-version-concurrency-control-mvcc" class="position-relative d-flex align-items-center group"> Multi-Version Concurrency Control (MVCC) <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="multi-version-concurrency-control-mvcc" aria-haspopup="dialog" aria-label="Share link: Multi-Version Concurrency Control (MVCC)"> Share link </button> </h4>Used for snapshot isolation and repeatable read: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback">Transaction Timeline: T1: BEGIN (snapshot at timestamp 100) T2: BEGIN (snapshot at timestamp 101) T1: MATCH (p:Person {id: 1}) RETURN p.balance -- Reads version at timestamp 100 T2: MATCH (p:Person {id: 1}) SET p.balance = 500 -- Creates new version at timestamp 101 T2: COMMIT (version 101 becomes visible) T1: MATCH (p:Person {id: 1}) RETURN p.balance -- Still reads version at timestamp 100 T1: COMMIT </code></pre></div>Benefits of MVCC: <ul> <li>Readers never block writers</li> <li>Writers never block readers</li> <li>No read locks required</li> <li>Excellent concurrency for read-heavy workloads</li> </ul> <h4 id="pessimistic-locking" class="position-relative d-flex align-items-center group"> Pessimistic Locking <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="pessimistic-locking" aria-haspopup="dialog" aria-label="Share link: Pessimistic Locking"> Share link </button> </h4>Used for serializable isolation: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Serializable isolation uses locks BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; -- Acquires shared lock for reads MATCH (a:Account {id: $account_id}) RETURN a.balance; -- Acquires exclusive lock for writes MATCH (a:Account {id: $account_id}) SET a.balance = a.balance - $amount; -- Locks held until commit COMMIT; -- Releases all locks </code></pre></div>Lock types: <ul> <li>Shared locks (S): Multiple transactions can hold shared locks simultaneously for reads</li> <li>Exclusive locks (X): Only one transaction can hold an exclusive lock for writes</li> <li>Intent locks: Hierarchical locks on graphs/nodes to improve performance</li> </ul> <h4 id="optimistic-concurrency-control" class="position-relative d-flex align-items-center group"> Optimistic Concurrency Control <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="optimistic-concurrency-control" aria-haspopup="dialog" aria-label="Share link: Optimistic Concurrency Control"> Share link </button> </h4>Used for high-contention scenarios with snapshot isolation: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Optimistic approach with version checking BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; -- Read current version MATCH (p:Product {sku: $sku}) RETURN p.inventory, p.version; -- Update with version check MATCH (p:Product {sku: $sku}) WHERE p.version = $expected_version SET p.inventory = $new_inventory, p.version = $expected_version + 1; -- If another transaction updated first, WHERE clause fails -- Transaction can detect conflict and retry COMMIT; </code></pre></div> <h3 id="practical-examples" class="position-relative d-flex align-items-center group"> Practical Examples <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="practical-examples" aria-haspopup="dialog" aria-label="Share link: Practical Examples"> Share link </button> </h3> <h4 id="preventing-lost-updates" class="position-relative d-flex align-items-center group"> Preventing Lost Updates <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="preventing-lost-updates" aria-haspopup="dialog" aria-label="Share link: Preventing Lost Updates"> Share link </button> </h4>Without proper isolation, concurrent updates can be lost: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Transaction 1: Transfer from Account A to B BEGIN; MATCH (a:Account {id: 'A'}) SET a.balance = a.balance - 100; -- Balance: $1000 -> $900 COMMIT; -- Transaction 2: Transfer from Account A to C (concurrent) BEGIN; MATCH (a:Account {id: 'A'}) SET a.balance = a.balance - 50; -- Reads $1000, sets to $950 (loses T1's update!) COMMIT; </code></pre></div>Use proper isolation to prevent: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Transaction 1 with serializable isolation BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; MATCH (a:Account {id: 'A'}) SET a.balance = a.balance - 100; COMMIT; -- Transaction 2 blocks until T1 completes BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; MATCH (a:Account {id: 'A'}) -- Waits for T1 to commit SET a.balance = a.balance - 50; -- Now correctly sees $900, sets to $850 COMMIT; </code></pre></div> <h4 id="preventing-phantom-reads" class="position-relative d-flex align-items-center group"> Preventing Phantom Reads <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="preventing-phantom-reads" aria-haspopup="dialog" aria-label="Share link: Preventing Phantom Reads"> Share link </button> </h4><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Transaction 1: Count high-value customers BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED; MATCH (c:Customer) WHERE c.lifetime_value > 10000 RETURN count(c); -- Returns 5 -- Transaction 2: Add new high-value customer (concurrent) BEGIN; CREATE (:Customer {name: 'New VIP', lifetime_value: 15000}); COMMIT; -- Transaction 1: Repeat count MATCH (c:Customer) WHERE c.lifetime_value > 10000 RETURN count(c); -- Returns 6 (phantom read!) COMMIT; </code></pre></div>Prevent with snapshot isolation: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Transaction 1 with snapshot isolation BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; MATCH (c:Customer) WHERE c.lifetime_value > 10000 RETURN count(c); -- Returns 5 -- Transaction 2: Add new high-value customer (concurrent) BEGIN; CREATE (:Customer {name: 'New VIP', lifetime_value: 15000}); COMMIT; -- Transaction 1: Repeat count sees same snapshot MATCH (c:Customer) WHERE c.lifetime_value > 10000 RETURN count(c); -- Still returns 5 (no phantom) COMMIT; </code></pre></div> <h4 id="preventing-write-skew" class="position-relative d-flex align-items-center group"> Preventing Write Skew <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="preventing-write-skew" aria-haspopup="dialog" aria-label="Share link: Preventing Write Skew"> Share link </button> </h4>Write skew occurs when concurrent transactions read overlapping data and make conflicting updates: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Constraint: At least one doctor must be on call -- Initially: Doctor A and B are both on call -- Transaction 1: Doctor A goes off call BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; MATCH (d:Doctor) WHERE d.on_call = true RETURN count(d); -- Returns 2, seems safe to go off call MATCH (da:Doctor {name: 'Dr. A'}) SET da.on_call = false; -- Now only 1 doctor on call (still safe) COMMIT; -- Transaction 2: Doctor B goes off call (concurrent) BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT; MATCH (d:Doctor) WHERE d.on_call = true RETURN count(d); -- Returns 2, seems safe to go off call MATCH (db:Doctor {name: 'Dr. B'}) SET db.on_call = false; -- Now 0 doctors on call (constraint violated!) COMMIT; </code></pre></div>Prevent with serializable isolation: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Transaction 1 with serializable BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; MATCH (d:Doctor) WHERE d.on_call = true RETURN count(d); -- Returns 2 MATCH (da:Doctor {name: 'Dr. A'}) SET da.on_call = false; COMMIT; -- Transaction 2 blocks until T1 completes BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; MATCH (d:Doctor) WHERE d.on_call = true RETURN count(d); -- Returns 1 (after T1 committed) -- Sees constraint would be violated, can abort ROLLBACK; </code></pre></div> <h3 id="configuration" class="position-relative d-flex align-items-center group"> Configuration <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="configuration" aria-haspopup="dialog" aria-label="Share link: Configuration"> Share link </button> </h3> <h4 id="setting-default-isolation-level" class="position-relative d-flex align-items-center group"> Setting Default Isolation Level <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="setting-default-isolation-level" aria-haspopup="dialog" aria-label="Share link: Setting Default Isolation Level"> Share link </button> </h4><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-bash" data-lang="bash"># Set default isolation level for all connections geode serve --default-isolation-level=snapshot # Per-connection isolation level geode shell --isolation-level=serializable </code></pre></div> <h4 id="isolation-level-per-session" class="position-relative d-flex align-items-center group"> Isolation Level Per Session <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="isolation-level-per-session" aria-haspopup="dialog" aria-label="Share link: Isolation Level Per Session"> Share link </button> </h4><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">-- Change isolation level for current session SET TRANSACTION ISOLATION LEVEL SNAPSHOT; -- All subsequent transactions use snapshot isolation BEGIN; MATCH (p:Person) RETURN p; COMMIT; -- Reset to default SET TRANSACTION ISOLATION LEVEL DEFAULT; </code></pre></div> <h4 id="deadlock-detection" class="position-relative d-flex align-items-center group"> Deadlock Detection <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="deadlock-detection" aria-haspopup="dialog" aria-label="Share link: Deadlock Detection"> Share link </button> </h4><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-bash" data-lang="bash"># Configure deadlock detection geode serve --deadlock-detection=enabled \ --deadlock-timeout=10s \ --deadlock-retry-attempts=3 </code></pre></div>When deadlock is detected: <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-gql" data-lang="gql">BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; -- Transaction acquires locks that create a deadlock cycle -- Geode detects deadlock after timeout -- Error: Deadlock detected, transaction aborted -- Application should retry BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE; -- Retry logic COMMIT; </code></pre></div> <h3 id="performance-considerations" class="position-relative d-flex align-items-center group"> Performance Considerations <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="performance-considerations" aria-haspopup="dialog" aria-label="Share link: Performance Considerations"> Share link </button> </h3> <h4 id="choosing-the-right-isolation-level" class="position-relative d-flex align-items-center group"> Choosing the Right Isolation Level <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="choosing-the-right-isolation-level" aria-haspopup="dialog" aria-label="Share link: Choosing the Right Isolation Level"> Share link </button> </h4><table> <thead> <tr> <th>Isolation Level</th> <th>Read Throughput</th> <th>Write Throughput</th> <th>Latency</th> <th>Consistency</th> </tr> </thead> <tbody> <tr> <td>Read Uncommitted</td> <td>Highest</td> <td>Highest</td> <td>Lowest</td> <td>Lowest</td> </tr> <tr> <td>Read Committed</td> <td>High</td> <td>High</td> <td>Low</td> <td>Medium</td> </tr> <tr> <td>Repeatable Read</td> <td>Medium</td> <td>Medium</td> <td>Medium</td> <td>High</td> </tr> <tr> <td>Snapshot</td> <td>High</td> <td>High</td> <td>Low</td> <td>High</td> </tr> <tr> <td>Serializable</td> <td>Low</td> <td>Low</td> <td>High</td> <td>Highest</td> </tr> </tbody> </table> <h4 id="performance-best-practices" class="position-relative d-flex align-items-center group"> Performance Best Practices <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="performance-best-practices" aria-haspopup="dialog" aria-label="Share link: Performance Best Practices"> Share link </button> </h4><ol> <li>Use Snapshot Isolation for most workloads: Best balance of consistency and performance</li> <li>Reserve Serializable for critical operations: Financial transactions, inventory management</li> <li>Keep transactions short: Reduces lock contention and blocking</li> <li>Read before write: Minimize time holding write locks</li> <li>Batch operations: Group related updates into single transaction</li> <li>Avoid long-running transactions: Can block other transactions and prevent garbage collection</li> </ol> <h4 id="monitoring-isolation-performance" class="position-relative d-flex align-items-center group"> Monitoring Isolation Performance <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="monitoring-isolation-performance" aria-haspopup="dialog" aria-label="Share link: Monitoring Isolation Performance"> Share link </button> </h4><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-bash" data-lang="bash"># Monitor transaction statistics geode stats --component=transactions \ --metrics=isolation_level,conflicts,retries,deadlocks # Example output: # Isolation Level | Transactions | Conflicts | Retries | Deadlocks # READ_COMMITTED | 1,234,567 | 45 | 12 | 0 # SNAPSHOT | 5,678,901 | 234 | 67 | 0 # SERIALIZABLE | 123,456 | 1,234 | 456 | 12 </code></pre></div> <h3 id="troubleshooting" class="position-relative d-flex align-items-center group"> Troubleshooting <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="troubleshooting" aria-haspopup="dialog" aria-label="Share link: Troubleshooting"> Share link </button> </h3> <h4 id="high-conflict-rate" class="position-relative d-flex align-items-center group"> High Conflict Rate <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="high-conflict-rate" aria-haspopup="dialog" aria-label="Share link: High Conflict Rate"> Share link </button> </h4>If seeing many conflicts with snapshot/serializable isolation: <ol> <li>Reduce transaction scope: Break large transactions into smaller ones</li> <li>Increase retry logic: Implement exponential backoff for retries</li> <li>Consider read committed: If strict consistency not required</li> <li>Partition data: Reduce contention by sharding hot data</li> </ol> <h4 id="deadlocks" class="position-relative d-flex align-items-center group"> Deadlocks <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="deadlocks" aria-haspopup="dialog" aria-label="Share link: Deadlocks"> Share link </button> </h4>If experiencing deadlocks: <ol> <li>Access resources in consistent order: Always lock nodes/relationships in same order</li> <li>Reduce lock hold time: Keep transactions as short as possible</li> <li>Lower isolation level: Use snapshot instead of serializable if possible</li> <li>Implement retry logic: Automatically retry deadlocked transactions</li> </ol> <h4 id="performance-degradation" class="position-relative d-flex align-items-center group"> Performance Degradation <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="performance-degradation" aria-haspopup="dialog" aria-label="Share link: Performance Degradation"> Share link </button> </h4>If isolation causing performance issues: <ol> <li>Profile transactions: Identify which transactions are slowest</li> <li>Reduce isolation level: Use lowest level that meets consistency requirements</li> <li>Optimize queries: Ensure efficient query plans to reduce lock time</li> <li>Scale horizontally: Add more replicas for read-heavy workloads</li> </ol> <h3 id="related-topics" class="position-relative d-flex align-items-center group"> Related Topics <button type="button" class="h-share btn btn-link p-0 text-decoration-none link-secondary opacity-50 hover-opacity-100 transition-all ms-1" data-share-target="related-topics" aria-haspopup="dialog" aria-label="Share link: Related Topics"> Share link </button> </h3><ul> <li><a href="/tags/transactions/" >Transactions</a> - Transaction management and ACID properties</li> <li><a href="/tags/data-integrity/" >Data Integrity</a> - Ensuring data consistency</li> <li><a href="/tags/sessions/" >Sessions</a> - Session management and connection settings</li> <li><a href="/tags/configuration/" >Configuration</a> - Transaction configuration options</li> <li><a href="/tags/performance/" >Performance</a> - Performance tuning and optimization</li> <li><a href="/docs/transactions/advanced-patterns/" >Transaction Patterns</a> - Advanced transaction patterns</li> </ul>

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