feat(transactions): add single-node transaction support with session-aware reads, commits, aborts, and transaction metrics

changelog.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 2026-04-29 - 2.8.0 - feat(transactions)
+add single-node transaction support with session-aware reads, commits, aborts, and transaction metrics
+
+- Buffer insert, update, delete, find, count, distinct, and findAndModify operations inside driver sessions and apply them on commit with write-conflict checks
+- Return MongoDB-compatible NoSuchTransaction and WriteConflict errors for transaction lifecycle failures
+- Expose authenticated users in connectionStatus and add session, transaction, auth, and oplog data to serverStatus and management metrics
+- Document transaction support and extend bridge metrics typings and integration tests accordingly
+
 ## 2026-04-29 - 2.7.1 - fix(repo)
 no changes to commit
 

readme.md

@@ -290,10 +290,12 @@ await client.connect();
 
 TLS is available for TCP listeners. `getConnectionUri()` includes `?tls=true` when TLS is enabled; pass the trusted CA to the MongoDB driver with `tlsCAFile`, `ca`, or `secureContext`.
 
-Authentication verifies SCRAM credentials, denies unauthenticated commands, and enforces command-level built-in roles for supported operations.
+Authentication verifies SCRAM credentials, denies unauthenticated commands, and enforces command-level built-in roles for supported operations. `connectionStatus` reports the authenticated users and roles for the current socket.
 
 Supported built-in role names are `root`, `read`, `readWrite`, `dbAdmin`, `userAdmin`, `clusterMonitor`, plus `readAnyDatabase`, `readWriteAnyDatabase`, `dbAdminAnyDatabase`, and `userAdminAnyDatabase`. When `usersPath` is set, SmartDB persists SCRAM credential material atomically and does not store plaintext passwords.
 
+Single-node transactions are supported through official MongoDB driver sessions. Writes with `startTransaction` and `autocommit: false` are buffered per logical session, reads inside the transaction see the buffered overlay, `commitTransaction` applies the write set with conflict checks, and `abortTransaction` discards it.
+
 Basic user management commands are available for authenticated users with `root` or `userAdmin` privileges:
 
 ```typescript
@@ -317,7 +319,7 @@ await client.db('admin').command({ usersInfo: 'reader' });
 | `port` | `number` | Configured port (TCP mode) |
 | `host` | `string` | Configured host (TCP mode) |
 | `socketPath` | `string \| undefined` | Socket path (socket mode) |
-| `getMetrics()` | `Promise<ISmartDbMetrics>` | Server metrics (db/collection counts, uptime) |
+| `getMetrics()` | `Promise<ISmartDbMetrics>` | Server metrics (db/collection counts, sessions, transactions, auth, uptime) |
 | `getOpLog(params?)` | `Promise<IOpLogResult>` | Query oplog entries with optional filters |
 | `getOpLogStats()` | `Promise<IOpLogStats>` | Aggregate oplog statistics |
 | `revertToSeq(seq, dryRun?)` | `Promise<IRevertResult>` | Revert to a specific oplog sequence |
@@ -531,7 +533,7 @@ const names = await collection.distinct('name');
 | **Aggregation** | `aggregate`, `count`, `distinct` |
 | **Indexes** | `createIndexes`, `dropIndexes`, `listIndexes` |
 | **Sessions** | `startSession`, `endSessions` |
-| **Transactions** | `commitTransaction`, `abortTransaction` |
+| **Transactions** | `startTransaction`, `commitTransaction`, `abortTransaction` through driver sessions |
 | **Admin** | `ping`, `listDatabases`, `listCollections`, `drop`, `dropDatabase`, `create`, `serverStatus`, `buildInfo`, `dbStats`, `collStats`, `connectionStatus`, `currentOp`, `renameCollection` |
 
 Compatible with wire protocol versions 0–21 (driver versions 3.6 through 7.0).
@@ -540,7 +542,7 @@ Compatible with wire protocol versions 0–21 (driver versions 3.6 through 7.0).
 
 ## Rust Crate Architecture 🦀
 
-The Rust engine is organized as a Cargo workspace with 8 focused crates:
+The Rust engine is organized as a Cargo workspace with 9 focused crates:
 
 | Crate | Purpose |
 |---|---|
@@ -551,6 +553,7 @@ The Rust engine is organized as a Cargo workspace with 8 focused crates:
 | `rustdb-storage` | Storage backends (memory, file), OpLog with point-in-time replay |
 | `rustdb-index` | B-tree/hash indexes, query planner (IXSCAN/COLLSCAN) |
 | `rustdb-txn` | Transaction + session management with snapshot isolation |
+| `rustdb-auth` | SCRAM-SHA-256 credential handling, user metadata persistence, RBAC checks |
 | `rustdb-commands` | 40+ command handlers wiring everything together |
 
 Cross-compiled for `linux_amd64` and `linux_arm64` via [@git.zone/tsrust](https://www.npmjs.com/package/@git.zone/tsrust).
@@ -563,6 +566,7 @@ The Bitcask-style file storage engine includes several reliability features:
 - **CRC32 checksums** — every record is integrity-checked on read
 - **Automatic compaction** — dead records are reclaimed when they exceed 50% of file size, runs on startup and after every write
 - **Hint file staleness detection** — the hint file records the data file size at write time; if data.rdb changed since (e.g. crash after a delete), the engine falls back to a full scan to ensure tombstones are not lost
+- **Torn-tail repair** — startup scans `data.rdb` to the last valid record, truncates invalid trailing bytes, and preserves all verified records after interrupted writes
 - **Stale socket cleanup** — orphaned `/tmp/smartdb-*.sock` files from crashed instances are automatically cleaned up on startup
 
 ### Data Integrity CLI 🔍

rust/crates/rustdb-auth/src/lib.rs

@@ -150,6 +150,13 @@ impl AuthEngine {
         self.enabled
     }
 
+    pub fn user_count(&self) -> usize {
+        self.users
+            .read()
+            .unwrap_or_else(|poisoned| poisoned.into_inner())
+            .len()
+    }
+
     pub fn supported_mechanisms(&self, namespace_user: &str) -> Vec<String> {
         let Some((database, username)) = namespace_user.split_once('.') else {
             return Vec::new();

rust/crates/rustdb-commands/src/error.rs

@@ -18,6 +18,12 @@ pub enum CommandError {
     #[error("transaction error: {0}")]
     TransactionError(String),
 
+    #[error("no such transaction: {0}")]
+    NoSuchTransaction(String),
+
+    #[error("write conflict: {0}")]
+    WriteConflict(String),
+
     #[error("namespace not found: {0}")]
     NamespaceNotFound(String),
 
@@ -52,6 +58,8 @@ impl CommandError {
             CommandError::StorageError(_) => (1, "InternalError"),
             CommandError::IndexError(_) => (27, "IndexNotFound"),
             CommandError::TransactionError(_) => (112, "WriteConflict"),
+            CommandError::NoSuchTransaction(_) => (251, "NoSuchTransaction"),
+            CommandError::WriteConflict(_) => (112, "WriteConflict"),
             CommandError::NamespaceNotFound(_) => (26, "NamespaceNotFound"),
             CommandError::NamespaceExists(_) => (48, "NamespaceExists"),
             CommandError::DuplicateKey(_) => (11000, "DuplicateKey"),
@@ -79,7 +87,15 @@ impl From<rustdb_storage::StorageError> for CommandError {
 
 impl From<rustdb_txn::TransactionError> for CommandError {
     fn from(e: rustdb_txn::TransactionError) -> Self {
-        CommandError::TransactionError(e.to_string())
+        match e {
+            rustdb_txn::TransactionError::NotFound(message) => {
+                CommandError::NoSuchTransaction(message)
+            }
+            rustdb_txn::TransactionError::WriteConflict(message) => {
+                CommandError::WriteConflict(message)
+            }
+            other => CommandError::TransactionError(other.to_string()),
+        }
     }
 }
 

rust/crates/rustdb-commands/src/handlers/admin_handler.rs

@@ -2,8 +2,9 @@ use bson::{doc, Bson, Document};
 use rustdb_index::IndexEngine;
 use tracing::debug;
 
-use crate::context::{CommandContext, CursorState};
+use crate::context::{CommandContext, ConnectionState, CursorState};
 use crate::error::{CommandError, CommandResult};
+use crate::transactions;
 
 /// Handle various admin / diagnostic / session / auth commands.
 pub async fn handle(
@@ -11,6 +12,7 @@ pub async fn handle(
     db: &str,
     ctx: &CommandContext,
     command_name: &str,
+    connection: &ConnectionState,
 ) -> CommandResult<Document> {
     match command_name {
         "ping" => Ok(doc! { "ok": 1.0 }),
@@ -24,13 +26,7 @@ pub async fn handle(
             "ok": 1.0,
         }),
 
-        "serverStatus" => Ok(doc! {
-            "host": "localhost",
-            "version": "7.0.0",
-            "process": "rustdb",
-            "uptime": ctx.start_time.elapsed().as_secs() as i64,
-            "ok": 1.0,
-        }),
+        "serverStatus" => handle_server_status(ctx),
 
         "hostInfo" => Ok(doc! {
             "system": {
@@ -90,13 +86,7 @@ pub async fn handle(
             "codeName": "CommandNotFound",
         }),
 
-        "connectionStatus" => Ok(doc! {
-            "authInfo": {
-                "authenticatedUsers": [],
-                "authenticatedUserRoles": [],
-            },
-            "ok": 1.0,
-        }),
+        "connectionStatus" => Ok(handle_connection_status(connection)),
 
         "createUser" => handle_create_user(cmd, db, ctx).await,
 
@@ -156,9 +146,9 @@ pub async fn handle(
             Ok(doc! { "ok": 1.0 })
         }
 
-        "commitTransaction" | "abortTransaction" => Err(CommandError::IllegalOperation(
-            "Transaction numbers are only allowed on a replica set member or mongos".into(),
-        )),
+        "commitTransaction" => transactions::commit_transaction_command(cmd, ctx).await,
+
+        "abortTransaction" => transactions::abort_transaction_command(cmd, ctx),
 
         // Auth stubs - accept silently.
         "saslStart" => Ok(doc! {
@@ -195,6 +185,72 @@ pub async fn handle(
     }
 }
 
+fn handle_server_status(ctx: &CommandContext) -> CommandResult<Document> {
+    let oplog_stats = ctx.oplog.stats();
+    Ok(doc! {
+        "host": "localhost",
+        "version": "7.0.0",
+        "process": "rustdb",
+        "uptime": ctx.start_time.elapsed().as_secs() as i64,
+        "connections": {
+            "current": 0_i32,
+            "available": i32::MAX,
+        },
+        "logicalSessionRecordCache": {
+            "activeSessionsCount": ctx.sessions.len() as i64,
+        },
+        "transactions": {
+            "currentActive": ctx.transactions.len() as i64,
+        },
+        "oplog": {
+            "currentSeq": oplog_stats.current_seq as i64,
+            "totalEntries": oplog_stats.total_entries as i64,
+            "oldestSeq": oplog_stats.oldest_seq as i64,
+            "entriesByOp": {
+                "insert": oplog_stats.inserts as i64,
+                "update": oplog_stats.updates as i64,
+                "delete": oplog_stats.deletes as i64,
+            },
+        },
+        "security": {
+            "authentication": ctx.auth.enabled(),
+            "users": ctx.auth.user_count() as i64,
+        },
+        "ok": 1.0,
+    })
+}
+
+fn handle_connection_status(connection: &ConnectionState) -> Document {
+    let authenticated_users: Vec<Bson> = connection
+        .authenticated_users
+        .iter()
+        .map(|user| {
+            Bson::Document(doc! {
+                "user": user.username.clone(),
+                "db": user.database.clone(),
+            })
+        })
+        .collect();
+
+    let authenticated_roles: Vec<Bson> = connection
+        .authenticated_users
+        .iter()
+        .flat_map(|user| {
+            user.roles
+                .iter()
+                .map(|role| Bson::Document(role_to_document(&user.database, role)))
+        })
+        .collect();
+
+    doc! {
+        "authInfo": {
+            "authenticatedUsers": authenticated_users,
+            "authenticatedUserRoles": authenticated_roles,
+        },
+        "ok": 1.0,
+    }
+}
+
 async fn handle_create_user(
     cmd: &Document,
     db: &str,

rust/crates/rustdb-commands/src/handlers/delete_handler.rs

@@ -7,6 +7,7 @@ use tracing::debug;
 
 use crate::context::CommandContext;
 use crate::error::{CommandError, CommandResult};
+use crate::transactions;
 
 /// Handle the `delete` command.
 pub async fn handle(
@@ -36,6 +37,7 @@ pub async fn handle(
     );
 
     let ns_key = format!("{}.{}", db, coll);
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
     let mut total_deleted: i32 = 0;
     let mut write_errors: Vec<Document> = Vec::new();
 
@@ -69,7 +71,7 @@ pub async fn handle(
             _ => 0, // default: delete all matches
         };
 
-        match delete_matching(db, coll, &ns_key, &filter, limit, ctx).await {
+        match delete_matching(db, coll, &ns_key, &filter, limit, ctx, txn_id.as_deref()).await {
             Ok(count) => {
                 total_deleted += count;
             }
@@ -114,7 +116,24 @@ async fn delete_matching(
     filter: &Document,
     limit: i32,
     ctx: &CommandContext,
+    txn_id: Option<&str>,
 ) -> Result<i32, CommandError> {
+    if let Some(txn_id) = txn_id {
+        let docs = transactions::load_transaction_docs(ctx, txn_id, db, coll).await?;
+        let matched = QueryMatcher::filter(&docs, filter);
+        let to_delete: &[Document] = if limit == 1 && !matched.is_empty() {
+            &matched[..1]
+        } else {
+            &matched
+        };
+
+        for doc in to_delete {
+            transactions::record_delete(ctx, txn_id, db, coll, doc.clone()).await?;
+        }
+
+        return Ok(to_delete.len() as i32);
+    }
+
     // Check if the collection exists; if not, nothing to delete.
     match ctx.storage.collection_exists(db, coll).await {
         Ok(false) => return Ok(0),

rust/crates/rustdb-commands/src/handlers/find_handler.rs

@@ -7,6 +7,7 @@ use rustdb_query::{QueryMatcher, sort_documents, apply_projection, distinct_valu
 
 use crate::context::{CommandContext, CursorState};
 use crate::error::{CommandError, CommandResult};
+use crate::transactions;
 
 /// Atomic counter for generating unique cursor IDs.
 static CURSOR_ID_COUNTER: AtomicI64 = AtomicI64::new(1);
@@ -80,9 +81,14 @@ pub async fn handle(
     let limit = get_i64(cmd, "limit").unwrap_or(0).max(0) as usize;
     let batch_size = get_i32(cmd, "batchSize").unwrap_or(101).max(0) as usize;
     let single_batch = get_bool(cmd, "singleBatch").unwrap_or(false);
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
 
     // If the collection does not exist, return an empty cursor.
-    let exists = ctx.storage.collection_exists(db, coll).await?;
+    let exists = if txn_id.is_some() {
+        true
+    } else {
+        ctx.storage.collection_exists(db, coll).await?
+    };
     if !exists {
         return Ok(doc! {
             "cursor": {
@@ -96,7 +102,9 @@ pub async fn handle(
 
     // Try index-accelerated lookup.
     let index_key = format!("{}.{}", db, coll);
-    let docs = if let Some(idx_ref) = ctx.indexes.get(&index_key) {
+    let docs = if let Some(ref txn_id) = txn_id {
+        transactions::load_transaction_docs(ctx, txn_id, db, coll).await?
+    } else if let Some(idx_ref) = ctx.indexes.get(&index_key) {
         if let Some(candidate_ids) = idx_ref.find_candidate_ids(&filter) {
             debug!(
                 ns = %ns,
@@ -298,9 +306,14 @@ pub async fn handle_count(
     ctx: &CommandContext,
 ) -> CommandResult<Document> {
     let coll = get_str(cmd, "count").unwrap_or("unknown");
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
 
     // Check collection existence.
-    let exists = ctx.storage.collection_exists(db, coll).await?;
+    let exists = if txn_id.is_some() {
+        true
+    } else {
+        ctx.storage.collection_exists(db, coll).await?
+    };
     if !exists {
         return Ok(doc! { "n": 0_i64, "ok": 1.0 });
     }
@@ -309,6 +322,23 @@ pub async fn handle_count(
     let skip = get_i64(cmd, "skip").unwrap_or(0).max(0) as usize;
     let limit = get_i64(cmd, "limit").unwrap_or(0).max(0) as usize;
 
+    if let Some(ref txn_id) = txn_id {
+        let docs = transactions::load_transaction_docs(ctx, txn_id, db, coll).await?;
+        let filtered = if query.is_empty() {
+            docs
+        } else {
+            QueryMatcher::filter(&docs, &query)
+        };
+        let mut n = filtered.len().saturating_sub(skip);
+        if limit > 0 {
+            n = n.min(limit);
+        }
+        return Ok(doc! {
+            "n": n as i64,
+            "ok": 1.0,
+        });
+    }
+
     let count: u64 = if query.is_empty() && skip == 0 && limit == 0 {
         // Fast path: use storage-level count.
         ctx.storage.count(db, coll).await?
@@ -352,15 +382,24 @@ pub async fn handle_distinct(
     let key = get_str(cmd, "key").ok_or_else(|| {
         CommandError::InvalidArgument("distinct requires a 'key' field".into())
     })?;
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
 
     // Check collection existence.
-    let exists = ctx.storage.collection_exists(db, coll).await?;
+    let exists = if txn_id.is_some() {
+        true
+    } else {
+        ctx.storage.collection_exists(db, coll).await?
+    };
     if !exists {
         return Ok(doc! { "values": [], "ok": 1.0 });
     }
 
     let query = get_document(cmd, "query").cloned();
-    let docs = ctx.storage.find_all(db, coll).await?;
+    let docs = if let Some(txn_id) = txn_id {
+        transactions::load_transaction_docs(ctx, &txn_id, db, coll).await?
+    } else {
+        ctx.storage.find_all(db, coll).await?
+    };
     let values = distinct_values(&docs, key, query.as_ref());
 
     Ok(doc! {

rust/crates/rustdb-commands/src/handlers/insert_handler.rs

@@ -6,6 +6,7 @@ use tracing::debug;
 
 use crate::context::CommandContext;
 use crate::error::{CommandError, CommandResult};
+use crate::transactions;
 
 /// Handle the `insert` command.
 pub async fn handle(
@@ -48,8 +49,13 @@ pub async fn handle(
         "insert command"
     );
 
-    // Auto-create database and collection if they don't exist.
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
+
+    // Auto-create database and collection if they don't exist. Transactional
+    // writes defer collection creation until commit so abort remains clean.
+    if txn_id.is_none() {
         ensure_collection_exists(db, coll, ctx).await?;
+    }
 
     let ns_key = format!("{}.{}", db, coll);
     let mut inserted_count: i32 = 0;
@@ -84,6 +90,24 @@ pub async fn handle(
             }
         }
 
+        if let Some(ref txn_id) = txn_id {
+            match transactions::record_insert(ctx, txn_id, db, coll, doc.clone()).await {
+                Ok(_) => inserted_count += 1,
+                Err(e) => {
+                    write_errors.push(doc! {
+                        "index": idx as i32,
+                        "code": 11000_i32,
+                        "codeName": "DuplicateKey",
+                        "errmsg": e.to_string(),
+                    });
+                    if ordered {
+                        break;
+                    }
+                }
+            }
+            continue;
+        }
+
         // Attempt storage insert.
         match ctx.storage.insert_one(db, coll, doc.clone()).await {
             Ok(id_str) => {

rust/crates/rustdb-commands/src/handlers/update_handler.rs

@@ -7,6 +7,7 @@ use tracing::debug;
 
 use crate::context::CommandContext;
 use crate::error::{CommandError, CommandResult};
+use crate::transactions;
 
 /// Handle `update` and `findAndModify` commands.
 pub async fn handle(
@@ -47,8 +48,12 @@ async fn handle_update(
 
     debug!(db = db, collection = coll, count = updates.len(), "update command");
 
-    // Auto-create database and collection if needed.
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
+
+    // Transactional writes defer namespace creation until commit.
+    if txn_id.is_none() {
         ensure_collection_exists(db, coll, ctx).await?;
+    }
 
     let ns_key = format!("{}.{}", db, coll);
 
@@ -136,7 +141,7 @@ async fn handle_update(
             });
 
         // Load all documents and filter.
-        let all_docs = load_filtered_docs(db, coll, &filter, &ns_key, ctx).await?;
+        let all_docs = load_filtered_docs(db, coll, &filter, &ns_key, ctx, txn_id.as_deref()).await?;
 
         if all_docs.is_empty() && upsert {
             // Upsert: create a new document.
@@ -166,6 +171,30 @@ async fn handle_update(
                         }
                     }
 
+                    if let Some(ref txn_id) = txn_id {
+                        match transactions::record_insert(ctx, txn_id, db, coll, updated.clone()).await {
+                            Ok(_) => {
+                                total_n += 1;
+                                upserted_list.push(doc! {
+                                    "index": idx as i32,
+                                    "_id": new_id,
+                                });
+                            }
+                            Err(e) => {
+                                write_errors.push(doc! {
+                                    "index": idx as i32,
+                                    "code": 1_i32,
+                                    "codeName": "InternalError",
+                                    "errmsg": e.to_string(),
+                                });
+                                if ordered {
+                                    break;
+                                }
+                            }
+                        }
+                        continue;
+                    }
+
                     // Insert the new document.
                     match ctx.storage.insert_one(db, coll, updated.clone()).await {
                         Ok(id_str) => {
@@ -258,6 +287,38 @@ async fn handle_update(
                         }
 
                         let id_str = extract_id_string(matched_doc);
+                        if let Some(ref txn_id) = txn_id {
+                            match transactions::record_update(
+                                ctx,
+                                txn_id,
+                                db,
+                                coll,
+                                matched_doc.clone(),
+                                updated_doc.clone(),
+                            )
+                            .await
+                            {
+                                Ok(_) => {
+                                    total_n += 1;
+                                    if matched_doc != &updated_doc {
+                                        total_n_modified += 1;
+                                    }
+                                }
+                                Err(e) => {
+                                    write_errors.push(doc! {
+                                        "index": idx as i32,
+                                        "code": 1_i32,
+                                        "codeName": "InternalError",
+                                        "errmsg": e.to_string(),
+                                    });
+                                    if ordered {
+                                        break;
+                                    }
+                                }
+                            }
+                            continue;
+                        }
+
                         match ctx
                             .storage
                             .update_by_id(db, coll, &id_str, updated_doc.clone())
@@ -407,8 +468,12 @@ async fn handle_find_and_modify(
                 .collect()
         });
 
-    // Auto-create database and collection.
+    let txn_id = transactions::active_transaction_id(ctx, cmd);
+
+    // Transactional writes defer namespace creation until commit.
+    if txn_id.is_none() {
         ensure_collection_exists(db, coll, ctx).await?;
+    }
 
     let ns_key = format!("{}.{}", db, coll);
 
@@ -416,7 +481,7 @@ async fn handle_find_and_modify(
     drop(ctx.get_or_init_index_engine(db, coll).await);
 
     // Load and filter documents.
-    let mut matched = load_filtered_docs(db, coll, &query, &ns_key, ctx).await?;
+    let mut matched = load_filtered_docs(db, coll, &query, &ns_key, ctx, txn_id.as_deref()).await?;
 
     // Sort if specified.
     if let Some(ref sort_spec) = sort {
@@ -430,6 +495,21 @@ async fn handle_find_and_modify(
         // Remove operation.
         if let Some(ref doc) = target {
             let id_str = extract_id_string(doc);
+            if let Some(ref txn_id) = txn_id {
+                transactions::record_delete(ctx, txn_id, db, coll, doc.clone()).await?;
+
+                let value = apply_fields_projection(doc, &fields);
+
+                return Ok(doc! {
+                    "value": value,
+                    "lastErrorObject": {
+                        "n": 1_i32,
+                        "updatedExisting": false,
+                    },
+                    "ok": 1.0,
+                });
+            }
+
             ctx.storage.delete_by_id(db, coll, &id_str).await?;
 
             // Record in oplog.
@@ -503,6 +583,35 @@ async fn handle_find_and_modify(
         }
 
         let id_str = extract_id_string(&original_doc);
+        if let Some(ref txn_id) = txn_id {
+            transactions::record_update(
+                ctx,
+                txn_id,
+                db,
+                coll,
+                original_doc.clone(),
+                updated_doc.clone(),
+            )
+            .await?;
+
+            let return_doc = if return_new {
+                &updated_doc
+            } else {
+                &original_doc
+            };
+
+            let value = apply_fields_projection(return_doc, &fields);
+
+            return Ok(doc! {
+                "value": value,
+                "lastErrorObject": {
+                    "n": 1_i32,
+                    "updatedExisting": true,
+                },
+                "ok": 1.0,
+            });
+        }
+
         ctx.storage
             .update_by_id(db, coll, &id_str, updated_doc.clone())
             .await?;
@@ -563,6 +672,26 @@ async fn handle_find_and_modify(
             }
         }
 
+        if let Some(ref txn_id) = txn_id {
+            transactions::record_insert(ctx, txn_id, db, coll, updated_doc.clone()).await?;
+
+            let value = if return_new {
+                apply_fields_projection(&updated_doc, &fields)
+            } else {
+                Bson::Null
+            };
+
+            return Ok(doc! {
+                "value": value,
+                "lastErrorObject": {
+                    "n": 1_i32,
+                    "updatedExisting": false,
+                    "upserted": upserted_id,
+                },
+                "ok": 1.0,
+            });
+        }
+
         let inserted_id_str = ctx.storage
             .insert_one(db, coll, updated_doc.clone())
             .await?;
@@ -622,7 +751,17 @@ async fn load_filtered_docs(
     filter: &Document,
     ns_key: &str,
     ctx: &CommandContext,
+    txn_id: Option<&str>,
 ) -> CommandResult<Vec<Document>> {
+    if let Some(txn_id) = txn_id {
+        let docs = transactions::load_transaction_docs(ctx, txn_id, db, coll).await?;
+        return if filter.is_empty() {
+            Ok(docs)
+        } else {
+            Ok(QueryMatcher::filter(&docs, filter))
+        };
+    }
+
     // Try to use index to narrow candidates.
     let candidate_ids: Option<HashSet<String>> = ctx
         .indexes

rust/crates/rustdb-commands/src/lib.rs

@@ -1,6 +1,7 @@
 mod context;
 pub mod error;
 pub mod handlers;
+pub mod transactions;
 mod router;
 
 pub use context::{CommandContext, ConnectionState, CursorState};

rust/crates/rustdb-commands/src/router.rs

@@ -8,7 +8,7 @@ use rustdb_auth::AuthAction;
 
 use crate::context::{CommandContext, ConnectionState};
 use crate::error::CommandError;
-use crate::handlers;
+use crate::{handlers, transactions};
 
 /// Routes parsed wire protocol commands to the appropriate handler.
 pub struct CommandRouter {
@@ -55,11 +55,12 @@ impl CommandRouter {
             }
         }
 
-        if transaction_command_unsupported(command_name, &cmd.command) {
-            return CommandError::IllegalOperation(
-                "Transaction numbers are only allowed on a replica set member or mongos".into(),
-            )
-            .to_error_doc();
+        if let Err(e) = transactions::prepare_transaction_for_command(
+            &self.ctx,
+            &cmd.command,
+            command_name,
+        ) {
+            return e.to_error_doc();
         }
 
         // Extract session id if present, and touch the session.
@@ -136,7 +137,7 @@ impl CommandRouter {
             | "grantRolesToUser" | "revokeRolesFromUser"
             | "currentOp" | "killOp" | "top" | "profile"
             | "compact" | "reIndex" | "fsync" | "connPoolSync" => {
-                handlers::admin_handler::handle(&cmd.command, db, &self.ctx, command_name).await
+                handlers::admin_handler::handle(&cmd.command, db, &self.ctx, command_name, connection).await
             }
 
             // -- unknown command --
@@ -207,9 +208,3 @@ fn aggregate_writes(command: &Document) -> bool {
         _ => None,
     }).unwrap_or(false)
 }
-
-fn transaction_command_unsupported(command_name: &str, command: &Document) -> bool {
-    matches!(command_name, "commitTransaction" | "abortTransaction")
-        || matches!(command.get("startTransaction"), Some(Bson::Boolean(true)))
-        || matches!(command.get("autocommit"), Some(Bson::Boolean(false)))
-}

rust/crates/rustdb-commands/src/transactions.rs

@@ -0,0 +1,367 @@
+use bson::{doc, Bson, Document};
+use rustdb_storage::OpType;
+use rustdb_txn::{TransactionState, WriteEntry, WriteOp};
+
+use crate::context::CommandContext;
+use crate::error::{CommandError, CommandResult};
+
+pub fn command_starts_transaction(cmd: &Document) -> bool {
+    matches!(cmd.get("startTransaction"), Some(Bson::Boolean(true)))
+}
+
+pub fn command_uses_transaction(cmd: &Document) -> bool {
+    command_starts_transaction(cmd) || matches!(cmd.get("autocommit"), Some(Bson::Boolean(false)))
+}
+
+pub fn active_transaction_id(ctx: &CommandContext, cmd: &Document) -> Option<String> {
+    if !command_uses_transaction(cmd) {
+        return None;
+    }
+
+    let session_id = cmd
+        .get("lsid")
+        .and_then(rustdb_txn::SessionEngine::extract_session_id)?;
+    ctx.sessions.get_transaction_id(&session_id)
+}
+
+pub fn prepare_transaction_for_command(
+    ctx: &CommandContext,
+    cmd: &Document,
+    command_name: &str,
+) -> CommandResult<()> {
+    if matches!(command_name, "commitTransaction" | "abortTransaction") {
+        return Ok(());
+    }
+
+    let starts_transaction = command_starts_transaction(cmd);
+    let uses_transaction = command_uses_transaction(cmd);
+    if !uses_transaction {
+        return Ok(());
+    }
+
+    let session_id = session_id_from_command(cmd)?;
+    require_txn_number(cmd)?;
+    ctx.sessions.get_or_create_session(&session_id);
+
+    if starts_transaction {
+        let txn_id = ctx.transactions.start_transaction(&session_id)?;
+        ctx.sessions.start_transaction(&session_id, &txn_id)?;
+        return Ok(());
+    }
+
+    if ctx.sessions.get_transaction_id(&session_id).is_none() {
+        return Err(CommandError::NoSuchTransaction(format!(
+            "session {session_id} has no active transaction"
+        )));
+    }
+
+    Ok(())
+}
+
+pub async fn load_transaction_docs(
+    ctx: &CommandContext,
+    txn_id: &str,
+    db: &str,
+    coll: &str,
+) -> CommandResult<Vec<Document>> {
+    let ns = namespace(db, coll);
+    if !ctx.transactions.has_snapshot(txn_id, &ns) {
+        let docs = match ctx.storage.collection_exists(db, coll).await {
+            Ok(true) => ctx.storage.find_all(db, coll).await?,
+            Ok(false) => Vec::new(),
+            Err(_) => Vec::new(),
+        };
+        ctx.transactions.set_snapshot(txn_id, &ns, docs);
+    }
+
+    ctx.transactions
+        .get_snapshot(txn_id, &ns)
+        .ok_or_else(|| CommandError::NoSuchTransaction(txn_id.to_string()))
+}
+
+pub async fn record_insert(
+    ctx: &CommandContext,
+    txn_id: &str,
+    db: &str,
+    coll: &str,
+    doc: Document,
+) -> CommandResult<String> {
+    let id = document_id_string(&doc)?;
+    let docs = load_transaction_docs(ctx, txn_id, db, coll).await?;
+    if docs.iter().any(|existing| document_id_string(existing).ok().as_deref() == Some(id.as_str())) {
+        return Err(CommandError::DuplicateKey(format!(
+            "duplicate _id '{}' in transaction",
+            id
+        )));
+    }
+
+    ctx.transactions.record_write(
+        txn_id,
+        &namespace(db, coll),
+        &id,
+        WriteOp::Insert,
+        Some(doc),
+        None,
+    );
+    Ok(id)
+}
+
+pub async fn record_update(
+    ctx: &CommandContext,
+    txn_id: &str,
+    db: &str,
+    coll: &str,
+    original: Document,
+    updated: Document,
+) -> CommandResult<String> {
+    let id = document_id_string(&original)?;
+    ctx.transactions.record_write(
+        txn_id,
+        &namespace(db, coll),
+        &id,
+        WriteOp::Update,
+        Some(updated),
+        Some(original),
+    );
+    Ok(id)
+}
+
+pub async fn record_delete(
+    ctx: &CommandContext,
+    txn_id: &str,
+    db: &str,
+    coll: &str,
+    original: Document,
+) -> CommandResult<String> {
+    let id = document_id_string(&original)?;
+    ctx.transactions.record_write(
+        txn_id,
+        &namespace(db, coll),
+        &id,
+        WriteOp::Delete,
+        None,
+        Some(original),
+    );
+    Ok(id)
+}
+
+pub async fn commit_transaction_command(
+    cmd: &Document,
+    ctx: &CommandContext,
+) -> CommandResult<Document> {
+    let session_id = session_id_from_command(cmd)?;
+    let txn_id = ctx
+        .sessions
+        .get_transaction_id(&session_id)
+        .ok_or_else(|| CommandError::NoSuchTransaction(format!(
+            "session {session_id} has no active transaction"
+        )))?;
+    let state = ctx.transactions.take_transaction(&txn_id)?;
+
+    preflight_transaction(&state, ctx).await?;
+    apply_transaction(state, ctx).await?;
+    ctx.sessions.end_transaction(&session_id);
+
+    Ok(doc! { "ok": 1.0 })
+}
+
+pub fn abort_transaction_command(cmd: &Document, ctx: &CommandContext) -> CommandResult<Document> {
+    let session_id = session_id_from_command(cmd)?;
+    let txn_id = ctx
+        .sessions
+        .get_transaction_id(&session_id)
+        .ok_or_else(|| CommandError::NoSuchTransaction(format!(
+            "session {session_id} has no active transaction"
+        )))?;
+    ctx.transactions.abort_transaction(&txn_id)?;
+    ctx.sessions.end_transaction(&session_id);
+    Ok(doc! { "ok": 1.0 })
+}
+
+pub fn document_id_string(doc: &Document) -> CommandResult<String> {
+    match doc.get("_id") {
+        Some(Bson::ObjectId(oid)) => Ok(oid.to_hex()),
+        Some(Bson::String(s)) => Ok(s.clone()),
+        Some(other) => Ok(format!("{}", other)),
+        None => Err(CommandError::InvalidArgument("document missing _id field".into())),
+    }
+}
+
+fn session_id_from_command(cmd: &Document) -> CommandResult<String> {
+    cmd.get("lsid")
+        .and_then(rustdb_txn::SessionEngine::extract_session_id)
+        .ok_or_else(|| CommandError::InvalidArgument("transaction command requires lsid".into()))
+}
+
+fn require_txn_number(cmd: &Document) -> CommandResult<()> {
+    match cmd.get("txnNumber") {
+        Some(Bson::Int64(_)) | Some(Bson::Int32(_)) => Ok(()),
+        _ => Err(CommandError::InvalidArgument(
+            "transaction command requires txnNumber".into(),
+        )),
+    }
+}
+
+fn namespace(db: &str, coll: &str) -> String {
+    format!("{db}.{coll}")
+}
+
+async fn preflight_transaction(state: &TransactionState, ctx: &CommandContext) -> CommandResult<()> {
+    for (ns, writes) in &state.write_set {
+        let (db, coll) = split_namespace(ns)?;
+        drop(ctx.get_or_init_index_engine(db, coll).await);
+
+        for (doc_id, entry) in writes {
+            let current = current_doc(ctx, db, coll, doc_id).await?;
+            match entry.op {
+                WriteOp::Insert => {
+                    if current.is_some() {
+                        return Err(CommandError::DuplicateKey(format!(
+                            "duplicate _id '{}' on transaction commit",
+                            doc_id
+                        )));
+                    }
+                    if let Some(ref doc) = entry.doc {
+                        if let Some(engine) = ctx.indexes.get(ns) {
+                            engine.check_unique_constraints(doc)?;
+                        }
+                    }
+                }
+                WriteOp::Update => {
+                    assert_unchanged(doc_id, current.as_ref(), entry.original_doc.as_ref())?;
+                    if let (Some(current_doc), Some(updated_doc)) = (current.as_ref(), entry.doc.as_ref()) {
+                        if let Some(engine) = ctx.indexes.get(ns) {
+                            engine.check_unique_constraints_for_update(current_doc, updated_doc)?;
+                        }
+                    }
+                }
+                WriteOp::Delete => {
+                    assert_unchanged(doc_id, current.as_ref(), entry.original_doc.as_ref())?;
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+async fn apply_transaction(state: TransactionState, ctx: &CommandContext) -> CommandResult<()> {
+    let mut namespaces: Vec<_> = state.write_set.into_iter().collect();
+    namespaces.sort_by(|a, b| a.0.cmp(&b.0));
+
+    for (ns, writes) in namespaces {
+        let (db, coll) = split_namespace(&ns)?;
+        ensure_collection_exists(db, coll, ctx).await?;
+        drop(ctx.get_or_init_index_engine(db, coll).await);
+
+        let mut writes: Vec<(String, WriteEntry)> = writes.into_iter().collect();
+        writes.sort_by(|a, b| a.0.cmp(&b.0));
+
+        for (doc_id, entry) in writes {
+            match entry.op {
+                WriteOp::Insert => {
+                    let Some(doc) = entry.doc else { continue; };
+                    let inserted_id = ctx.storage.insert_one(db, coll, doc.clone()).await?;
+                    ctx.oplog.append(OpType::Insert, db, coll, &inserted_id, Some(doc.clone()), None);
+                    if let Some(mut engine) = ctx.indexes.get_mut(&ns) {
+                        engine.on_insert(&doc)?;
+                    }
+                }
+                WriteOp::Update => {
+                    let Some(doc) = entry.doc else { continue; };
+                    ctx.storage.update_by_id(db, coll, &doc_id, doc.clone()).await?;
+                    ctx.oplog.append(
+                        OpType::Update,
+                        db,
+                        coll,
+                        &doc_id,
+                        Some(doc.clone()),
+                        entry.original_doc.clone(),
+                    );
+                    if let (Some(mut engine), Some(ref original)) =
+                        (ctx.indexes.get_mut(&ns), entry.original_doc.as_ref())
+                    {
+                        engine.on_update(original, &doc)?;
+                    }
+                }
+                WriteOp::Delete => {
+                    ctx.storage.delete_by_id(db, coll, &doc_id).await?;
+                    ctx.oplog.append(
+                        OpType::Delete,
+                        db,
+                        coll,
+                        &doc_id,
+                        None,
+                        entry.original_doc.clone(),
+                    );
+                    if let (Some(mut engine), Some(ref original)) =
+                        (ctx.indexes.get_mut(&ns), entry.original_doc.as_ref())
+                    {
+                        engine.on_delete(original);
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+async fn current_doc(
+    ctx: &CommandContext,
+    db: &str,
+    coll: &str,
+    doc_id: &str,
+) -> CommandResult<Option<Document>> {
+    match ctx.storage.collection_exists(db, coll).await {
+        Ok(true) => Ok(ctx.storage.find_by_id(db, coll, doc_id).await?),
+        Ok(false) => Ok(None),
+        Err(_) => Ok(None),
+    }
+}
+
+fn assert_unchanged(
+    doc_id: &str,
+    current: Option<&Document>,
+    original: Option<&Document>,
+) -> CommandResult<()> {
+    if current == original {
+        return Ok(());
+    }
+
+    Err(CommandError::WriteConflict(format!(
+        "document '{}' changed during transaction",
+        doc_id
+    )))
+}
+
+async fn ensure_collection_exists(
+    db: &str,
+    coll: &str,
+    ctx: &CommandContext,
+) -> CommandResult<()> {
+    if let Err(e) = ctx.storage.create_database(db).await {
+        let msg = e.to_string();
+        if !msg.contains("AlreadyExists") && !msg.contains("already exists") {
+            return Err(CommandError::StorageError(msg));
+        }
+    }
+
+    match ctx.storage.collection_exists(db, coll).await {
+        Ok(true) => Ok(()),
+        Ok(false) | Err(_) => {
+            if let Err(e) = ctx.storage.create_collection(db, coll).await {
+                let msg = e.to_string();
+                if !msg.contains("AlreadyExists") && !msg.contains("already exists") {
+                    return Err(CommandError::StorageError(msg));
+                }
+            }
+            Ok(())
+        }
+    }
+}
+
+fn split_namespace(ns: &str) -> CommandResult<(&str, &str)> {
+    ns.split_once('.')
+        .ok_or_else(|| CommandError::InvalidArgument(format!("invalid namespace '{ns}'")))
+}

rust/crates/rustdb-txn/src/session.rs

@@ -170,6 +170,16 @@ impl SessionEngine {
         }
         count
     }
+
+    /// Number of currently tracked logical sessions.
+    pub fn len(&self) -> usize {
+        self.sessions.len()
+    }
+
+    /// Whether there are no tracked logical sessions.
+    pub fn is_empty(&self) -> bool {
+        self.sessions.is_empty()
+    }
 }
 
 impl Default for SessionEngine {

rust/crates/rustdb-txn/src/transaction.rs

@@ -18,7 +18,7 @@ pub enum TransactionStatus {
 }
 
 /// Describes a write operation within a transaction.
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum WriteOp {
     Insert,
     Update,
@@ -137,6 +137,25 @@ impl TransactionEngine {
         Ok(())
     }
 
+    /// Remove an active transaction and return its buffered state for an
+    /// external committer that needs to update secondary indexes and oplogs.
+    pub fn take_transaction(&self, txn_id: &str) -> TransactionResult<TransactionState> {
+        let state = self
+            .transactions
+            .remove(txn_id)
+            .map(|(_, s)| s)
+            .ok_or_else(|| TransactionError::NotFound(txn_id.to_string()))?;
+
+        if state.status != TransactionStatus::Active {
+            return Err(TransactionError::InvalidState(format!(
+                "transaction {} is {:?}, cannot commit",
+                txn_id, state.status
+            )));
+        }
+
+        Ok(state)
+    }
+
     /// Abort a transaction, discarding all buffered writes.
     pub fn abort_transaction(&self, txn_id: &str) -> TransactionResult<()> {
         let mut state = self
@@ -191,18 +210,31 @@ impl TransactionEngine {
         original: Option<Document>,
     ) {
         if let Some(mut state) = self.transactions.get_mut(txn_id) {
-            let entry = WriteEntry {
+            let writes = state.write_set.entry(ns.to_string()).or_default();
+            if let Some(existing) = writes.remove(doc_id) {
+                if let Some(merged) = merge_write_entry(existing, op, doc, original) {
+                    writes.insert(doc_id.to_string(), merged);
+                }
+            } else {
+                writes.insert(
+                    doc_id.to_string(),
+                    WriteEntry {
                         op,
                         doc,
                         original_doc: original,
-            };
-            state
-                .write_set
-                .entry(ns.to_string())
-                .or_default()
-                .insert(doc_id.to_string(), entry);
+                    },
+                );
             }
         }
+    }
+
+    /// Return true if the transaction already has a base snapshot for a namespace.
+    pub fn has_snapshot(&self, txn_id: &str, ns: &str) -> bool {
+        self.transactions
+            .get(txn_id)
+            .map(|state| state.snapshots.contains_key(ns))
+            .unwrap_or(false)
+    }
 
     /// Get a snapshot of documents for a namespace within a transaction,
     /// applying the write overlay (inserts, updates, deletes) on top.
@@ -270,6 +302,67 @@ impl TransactionEngine {
             state.snapshots.insert(ns.to_string(), docs);
         }
     }
+
+    /// Number of currently active transactions.
+    pub fn len(&self) -> usize {
+        self.transactions.len()
+    }
+
+    /// Whether there are no active transactions.
+    pub fn is_empty(&self) -> bool {
+        self.transactions.is_empty()
+    }
+}
+
+fn merge_write_entry(
+    existing: WriteEntry,
+    next_op: WriteOp,
+    next_doc: Option<Document>,
+    next_original: Option<Document>,
+) -> Option<WriteEntry> {
+    match (existing.op, next_op) {
+        (WriteOp::Insert, WriteOp::Update) => Some(WriteEntry {
+            op: WriteOp::Insert,
+            doc: next_doc,
+            original_doc: None,
+        }),
+        (WriteOp::Insert, WriteOp::Delete) => None,
+        (WriteOp::Insert, WriteOp::Insert) => Some(WriteEntry {
+            op: WriteOp::Insert,
+            doc: next_doc,
+            original_doc: None,
+        }),
+        (WriteOp::Update, WriteOp::Update) => Some(WriteEntry {
+            op: WriteOp::Update,
+            doc: next_doc,
+            original_doc: existing.original_doc,
+        }),
+        (WriteOp::Update, WriteOp::Delete) => Some(WriteEntry {
+            op: WriteOp::Delete,
+            doc: None,
+            original_doc: existing.original_doc,
+        }),
+        (WriteOp::Update, WriteOp::Insert) => Some(WriteEntry {
+            op: WriteOp::Update,
+            doc: next_doc,
+            original_doc: existing.original_doc,
+        }),
+        (WriteOp::Delete, WriteOp::Insert) => Some(WriteEntry {
+            op: if existing.original_doc.is_some() {
+                WriteOp::Update
+            } else {
+                WriteOp::Insert
+            },
+            doc: next_doc,
+            original_doc: existing.original_doc,
+        }),
+        (WriteOp::Delete, WriteOp::Update) => Some(WriteEntry {
+            op: WriteOp::Update,
+            doc: next_doc,
+            original_doc: existing.original_doc.or(next_original),
+        }),
+        (WriteOp::Delete, WriteOp::Delete) => Some(existing),
+    }
 }
 
 impl Default for TransactionEngine {

rust/crates/rustdb/src/management.rs

@@ -255,6 +255,10 @@ async fn handle_get_metrics(
                     "collections": total_collections,
                     "oplogEntries": oplog_stats.total_entries,
                     "oplogCurrentSeq": oplog_stats.current_seq,
+                    "sessions": ctx.sessions.len(),
+                    "activeTransactions": ctx.transactions.len(),
+                    "authEnabled": ctx.auth.enabled(),
+                    "authUsers": ctx.auth.user_count(),
                     "uptimeSeconds": uptime_secs,
                 }),
             )

test/test.auth.ts

@@ -88,6 +88,11 @@ tap.test('auth: should authenticate valid credentials', async () => {
   await authedClient.connect();
   const result = await authedClient.db('admin').command({ ping: 1 });
   expect(result.ok).toEqual(1);
+
+  const status = await authedClient.db('admin').command({ connectionStatus: 1 });
+  expect(status.ok).toEqual(1);
+  expect(status.authInfo.authenticatedUsers[0]).toEqual({ user: 'root', db: 'admin' });
+  expect(status.authInfo.authenticatedUserRoles[0]).toEqual({ role: 'root', db: 'admin' });
 });
 
 tap.test('auth: should allow CRUD after authentication', async () => {

test/test.transactions.ts

@@ -44,7 +44,7 @@ tap.test('transactions: should still support explicit sessions', async () => {
   expect(end.ok).toEqual(1);
 });
 
-tap.test('transactions: should reject raw transaction-scoped writes before mutation', async () => {
+tap.test('transactions: should reject transaction-scoped writes without txnNumber before mutation', async () => {
   const db = client.db('txntest');
   const coll = db.collection('docs');
   await coll.insertOne({ key: 'outside', value: 1 });
@@ -59,8 +59,8 @@ tap.test('transactions: should reject raw transaction-scoped writes before mutat
     });
   } catch (err: any) {
     threw = true;
-    expect(err.code).toEqual(20);
-    expect(err.codeName).toEqual('IllegalOperation');
+    expect(err.code).toEqual(14);
+    expect(err.codeName).toEqual('TypeMismatch');
   }
   expect(threw).toBeTrue();
 
@@ -68,44 +68,89 @@ tap.test('transactions: should reject raw transaction-scoped writes before mutat
   expect(await coll.countDocuments({ key: 'outside' })).toEqual(1);
 });
 
-tap.test('transactions: official driver transaction should fail without committing writes', async () => {
+tap.test('transactions: official driver transaction should commit buffered writes', async () => {
   const coll = client.db('txntest').collection('driverdocs');
   await coll.insertOne({ key: 'outside-driver', value: 0 });
   const session = client.startSession();
 
-  let threw = false;
   try {
     session.startTransaction();
     await coll.insertOne({ key: 'inside-driver', value: 1 }, { session });
+    const inTxn = await coll.findOne({ key: 'inside-driver' }, { session });
+    expect(inTxn).toBeTruthy();
+    expect(await coll.countDocuments({ key: 'inside-driver' })).toEqual(0);
     await session.commitTransaction();
-  } catch (err: any) {
-    threw = true;
-    expect(err.code).toEqual(20);
-    expect(err.codeName).toEqual('IllegalOperation');
-    await session.abortTransaction().catch(() => undefined);
   } finally {
     await session.endSession();
   }
 
-  expect(threw).toBeTrue();
-  expect(await coll.countDocuments({ key: 'inside-driver' })).toEqual(0);
+  expect(await coll.countDocuments({ key: 'inside-driver' })).toEqual(1);
   expect(await coll.countDocuments({ key: 'outside-driver' })).toEqual(1);
 });
 
-tap.test('transactions: commit and abort commands should be explicit unsupported errors', async () => {
+tap.test('transactions: abort should discard buffered writes', async () => {
+  const coll = client.db('txntest').collection('abortdocs');
+  const session = client.startSession();
+
+  try {
+    session.startTransaction();
+    await coll.insertOne({ key: 'abort-me', value: 1 }, { session });
+    expect(await coll.findOne({ key: 'abort-me' }, { session })).toBeTruthy();
+    await session.abortTransaction();
+  } finally {
+    await session.endSession();
+  }
+
+  expect(await coll.findOne({ key: 'abort-me' })).toBeNull();
+});
+
+tap.test('transactions: update and delete should commit atomically', async () => {
+  const coll = client.db('txntest').collection('mutations');
+  await coll.insertMany([
+    { key: 'update-me', value: 1 },
+    { key: 'delete-me', value: 2 },
+  ]);
+  const session = client.startSession();
+
+  try {
+    session.startTransaction();
+    await coll.updateOne({ key: 'update-me' }, { $set: { value: 10 } }, { session });
+    await coll.deleteOne({ key: 'delete-me' }, { session });
+    expect((await coll.findOne({ key: 'update-me' }, { session }))!.value).toEqual(10);
+    expect(await coll.findOne({ key: 'delete-me' }, { session })).toBeNull();
+    expect((await coll.findOne({ key: 'update-me' }))!.value).toEqual(1);
+    expect(await coll.findOne({ key: 'delete-me' })).toBeTruthy();
+    await session.commitTransaction();
+  } finally {
+    await session.endSession();
+  }
+
+  expect((await coll.findOne({ key: 'update-me' }))!.value).toEqual(10);
+  expect(await coll.findOne({ key: 'delete-me' })).toBeNull();
+});
+
+tap.test('transactions: commit and abort without active transaction should be explicit errors', async () => {
   for (const command of [{ commitTransaction: 1 }, { abortTransaction: 1 }]) {
     let threw = false;
     try {
       await client.db('admin').command(command);
     } catch (err: any) {
       threw = true;
-      expect(err.code).toEqual(20);
-      expect(err.codeName).toEqual('IllegalOperation');
+      expect(err.code).toEqual(251);
+      expect(err.codeName).toEqual('NoSuchTransaction');
     }
     expect(threw).toBeTrue();
   }
 });
 
+tap.test('transactions: serverStatus should expose transaction and oplog metrics', async () => {
+  const status = await client.db('admin').command({ serverStatus: 1 });
+  expect(status.ok).toEqual(1);
+  expect(status.transactions.currentActive).toEqual(0);
+  expect(status.logicalSessionRecordCache.activeSessionsCount).toBeGreaterThanOrEqual(0);
+  expect(status.oplog.totalEntries).toBeGreaterThan(0);
+});
+
 tap.test('transactions: cleanup', async () => {
   await client.close();
   await server.stop();

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartdb',
-  version: '2.7.1',
+  version: '2.8.0',
   description: 'A MongoDB-compatible embedded database server with wire protocol support, backed by a high-performance Rust engine.'
 }

ts/ts_smartdb/rust-db-bridge.ts

@@ -76,6 +76,10 @@ export interface ISmartDbMetrics {
   collections: number;
   oplogEntries: number;
   oplogCurrentSeq: number;
+  sessions: number;
+  activeTransactions: number;
+  authEnabled: boolean;
+  authUsers: number;
   uptimeSeconds: number;
 }