Add a new begin_latest_read api for transaction support

Signed-off-by: yongman <yming0221@gmail.com>

src/transaction/client.rs

@@ -276,12 +276,35 @@ impl Client {
         Ok(res)
     }
 
-    pub fn new_transaction(
-        &self,
-        timestamp: Timestamp,
-        options: TransactionOptions,
-    ) -> Transaction {
+    fn new_transaction(&self, timestamp: Timestamp, options: TransactionOptions) -> Transaction {
         let logger = self.logger.new(o!("child" => 1));
         Transaction::new(timestamp, self.pd.clone(), options, logger)
     }
+
+    /// Creates a new latest commit readonly [`Transaction`].
+    ///
+    /// Read operations will read the latest commit data which is not a snapshot read.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// # use tikv_client::{Config, TransactionClient};
+    /// # use futures::prelude::*;
+    /// # futures::executor::block_on(async {
+    /// let client = TransactionClient::new(vec!["192.168.0.100"], None)
+    ///     .await
+    ///     .unwrap();
+    /// let options = TransactionOptions::new_optimistic();
+    /// let mut transaction = client.begin_latest_read(options).await.unwrap();
+    /// // ... Issue some reads.
+    /// transaction.commit().await.unwrap();
+    /// # });
+    /// ```
+    pub fn begin_latest_read(&self, options: TransactionOptions) -> Transaction {
+        debug!(
+            self.logger,
+            "creating new latest commit readonly transaction"
+        );
+        self.new_transaction(Timestamp::from_version(u64::MAX), options.read_only())
+    }
 }

src/transaction/transaction.rs

@@ -113,7 +113,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn get(&mut self, key: impl Into<Key>) -> Result<Option<Value>> {
         debug!(self.logger, "invoking transactional get request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(true).await?;
         let timestamp = self.timestamp.clone();
         let rpc = self.rpc.clone();
         let key = key.into();
@@ -177,7 +177,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn get_for_update(&mut self, key: impl Into<Key>) -> Result<Option<Value>> {
         debug!(self.logger, "invoking transactional get_for_update request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         if !self.is_pessimistic() {
             let key = key.into();
             self.lock_keys(iter::once(key.clone())).await?;
@@ -244,7 +244,7 @@ impl<PdC: PdClient> Transaction<PdC> {
         keys: impl IntoIterator<Item = impl Into<Key>>,
     ) -> Result<impl Iterator<Item = KvPair>> {
         debug!(self.logger, "invoking transactional batch_get request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(true).await?;
         let timestamp = self.timestamp.clone();
         let rpc = self.rpc.clone();
         let retry_options = self.options.retry_options.clone();
@@ -299,7 +299,7 @@ impl<PdC: PdClient> Transaction<PdC> {
             self.logger,
             "invoking transactional batch_get_for_update request"
         );
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         let keys: Vec<Key> = keys.into_iter().map(|k| k.into()).collect();
         if !self.is_pessimistic() {
             self.lock_keys(keys.clone()).await?;
@@ -433,7 +433,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn put(&mut self, key: impl Into<Key>, value: impl Into<Value>) -> Result<()> {
         debug!(self.logger, "invoking transactional put request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         let key = key.into();
         if self.is_pessimistic() {
             self.pessimistic_lock(iter::once(key.clone()), false)
@@ -464,7 +464,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn insert(&mut self, key: impl Into<Key>, value: impl Into<Value>) -> Result<()> {
         debug!(self.logger, "invoking transactional insert request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         let key = key.into();
         if self.buffer.get(&key).is_some() {
             return Err(Error::DuplicateKeyInsertion);
@@ -499,7 +499,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn delete(&mut self, key: impl Into<Key>) -> Result<()> {
         debug!(self.logger, "invoking transactional delete request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         let key = key.into();
         if self.is_pessimistic() {
             self.pessimistic_lock(iter::once(key.clone()), false)
@@ -537,7 +537,7 @@ impl<PdC: PdClient> Transaction<PdC> {
         keys: impl IntoIterator<Item = impl Into<Key>>,
     ) -> Result<()> {
         debug!(self.logger, "invoking transactional lock_keys request");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(false).await?;
         match self.options.kind {
             TransactionKind::Optimistic => {
                 for key in keys {
@@ -569,6 +569,15 @@ impl<PdC: PdClient> Transaction<PdC> {
     /// ```
     pub async fn commit(&mut self) -> Result<Option<Timestamp>> {
         debug!(self.logger, "commiting transaction");
+
+        {
+            // readonly transaction no need to commit
+            let status = self.status.read().await;
+            if *status == TransactionStatus::ReadOnly {
+                return Ok(None);
+            }
+        }
+
         {
             let mut status = self.status.write().await;
             if !matches!(
@@ -677,7 +686,7 @@ impl<PdC: PdClient> Transaction<PdC> {
     #[doc(hidden)]
     pub async fn send_heart_beat(&mut self) -> Result<u64> {
         debug!(self.logger, "sending heart_beat");
-        self.check_allow_operation().await?;
+        self.check_allow_operation(true).await?;
         let primary_key = match self.buffer.get_primary_key() {
             Some(k) => k,
             None => return Err(Error::NoPrimaryKey),
@@ -703,7 +712,7 @@ impl<PdC: PdClient> Transaction<PdC> {
         key_only: bool,
         reverse: bool,
     ) -> Result<impl Iterator<Item = KvPair>> {
-        self.check_allow_operation().await?;
+        self.check_allow_operation(true).await?;
         let timestamp = self.timestamp.clone();
         let rpc = self.rpc.clone();
         let retry_options = self.options.retry_options.clone();
@@ -840,10 +849,17 @@ impl<PdC: PdClient> Transaction<PdC> {
     }
 
     /// Checks if the transaction can perform arbitrary operations.
-    async fn check_allow_operation(&self) -> Result<()> {
+    async fn check_allow_operation(&self, readonly: bool) -> Result<()> {
         let status = self.status.read().await;
         match *status {
-            TransactionStatus::ReadOnly | TransactionStatus::Active => Ok(()),
+            TransactionStatus::Active => Ok(()),
+            TransactionStatus::ReadOnly => {
+                if readonly {
+                    Ok(())
+                } else {
+                    Err(Error::OperationReadOnlyError)
+                }
+            }
             TransactionStatus::Committed
             | TransactionStatus::Rolledback
             | TransactionStatus::StartedCommit

tests/integration_tests.rs

@@ -17,9 +17,10 @@ use futures::prelude::*;
 use rand::{seq::IteratorRandom, thread_rng, Rng};
 use serial_test::serial;
 use std::{
+    assert_eq,
     collections::{HashMap, HashSet},
     convert::TryInto,
-    iter,
+    iter, matches,
 };
 use tikv_client::{
     transaction::HeartbeatOption, BoundRange, Error, Key, KvPair, RawClient, Result, Transaction,
@@ -942,6 +943,31 @@ async fn txn_key_exists() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+#[serial]
+async fn txn_latest_read() -> Result<()> {
+    init().await?;
+    let client = TransactionClient::new_with_config(pd_addrs(), Default::default(), None).await?;
+    let key = "key".to_owned();
+    let value = "value".to_owned();
+    let options = TransactionOptions::new_optimistic();
+    let mut t1 = client.begin_latest_read(options);
+    t1.get(key.clone()).await?;
+    t1.put(key.clone(), value.clone())
+        .await
+        .map_err(|_e| matches!(Error::OperationReadOnlyError, _e))
+        .unwrap_err();
+    // commit is no needed for readonly transaction, commit() will take no effect if called.
+    t1.commit().await?;
+
+    let options = TransactionOptions::new_pessimistic();
+    let mut t2 = client.begin_latest_read(options);
+    t2.get(key.clone()).await?;
+    // t2.commit().await?;
+
+    Ok(())
+}
+
 // helper function
 async fn get_u32(client: &RawClient, key: Vec<u8>) -> Result<u32> {
     let x = client.get(key).await?.unwrap();

tikv-client-common/src/errors.rs

@@ -22,6 +22,9 @@ pub enum Error {
     /// It's not allowed to perform operations in a transaction after it has been committed or rolled back.
     #[error("Cannot read or write data after any attempt to commit or roll back the transaction")]
     OperationAfterCommitError,
+    /// It's not allowed to perform write operation in a readonly transaction.
+    #[error("Cannot write data in read-only transaction")]
+    OperationReadOnlyError,
     /// We tried to use 1pc for a transaction, but it didn't work. Probably should have used 2pc.
     #[error("1PC transaction could not be committed.")]
     OnePcFailure,