refactor: do not use TxnPutRequest|TxnDeleteRequest.prev_value, alw…

…ays return previous value (databendlabs#14371)

Meta-service does not check `TxnPutRequest.prev_value` and
`TxnDeleteRequest.prev_value` any more, and always assumes it is true.
When a `Put` or `Delete` request is executed, the previous value before
`Put` will always be responded.

src/meta/client/src/lib.rs

@@ -93,6 +93,12 @@ pub static METACLI_COMMIT_SEMVER: LazyLock<Version> = LazyLock::new(|| {
 ///   client: remove using MetaGrpcReq::GetKV/MGetKV/ListKV;
 ///   client: remove falling back kv_read_v1(Streamed(List)) to kv_api(List), added in `2023-10-20: since 1.2.176`;
 ///
+/// - 2024-01-17: since TODO:
+///   server: do not use TxnPutRequest.prev_value;
+///   server: do not use TxnDeleteRequest.prev_value;
+///           Always return the previous value;
+///           field index is reserved, no compatibility changes.
+///
 /// Server feature set:
 /// ```yaml
 /// server_features:

src/meta/raft-store/src/applier.rs

@@ -394,11 +394,7 @@ impl<'a> Applier<'a> {
 
         let put_resp = TxnPutResponse {
             key: put.key.clone(),
-            prev_value: if put.prev_value {
-                prev.map(pb::SeqV::from)
-            } else {
-                None
-            },
+            prev_value: prev.map(pb::SeqV::from),
         };
 
         resp.responses.push(TxnOpResponse {
@@ -428,11 +424,7 @@ impl<'a> Applier<'a> {
         let del_resp = TxnDeleteResponse {
             key: delete.key.clone(),
             success: is_deleted,
-            prev_value: if delete.prev_value {
-                prev.map(pb::SeqV::from)
-            } else {
-                None
-            },
+            prev_value: prev.map(pb::SeqV::from),
         };
 
         resp.responses.push(TxnOpResponse {

src/meta/raft-store/src/state_machine/sm.rs

@@ -549,11 +549,7 @@ impl StateMachine {
 
         let put_resp = TxnPutResponse {
             key: put.key.clone(),
-            prev_value: if put.prev_value {
-                prev.map(pb::SeqV::from)
-            } else {
-                None
-            },
+            prev_value: prev.map(pb::SeqV::from),
         };
 
         resp.responses.push(TxnOpResponse {
@@ -590,11 +586,7 @@ impl StateMachine {
         let del_resp = TxnDeleteResponse {
             key: delete.key.clone(),
             success: is_deleted,
-            prev_value: if delete.prev_value {
-                prev.map(pb::SeqV::from)
-            } else {
-                None
-            },
+            prev_value: prev.map(pb::SeqV::from),
         };
 
         resp.responses.push(TxnOpResponse {

src/meta/types/proto/request.proto

@@ -44,6 +44,7 @@ message TxnPutRequest {
   bytes value = 2;
 
   // Whether or not to return the prev value
+  // Not used anymore
   bool prev_value = 3;
 
   // Absolute expire time
@@ -64,7 +65,9 @@ message TxnPutResponse {
 // Delete request and response
 message TxnDeleteRequest {
   string key = 1;
+
   // if or not return the prev value
+  // Not used anymore
   bool prev_value = 2;
 
   // Delete only if the `seq` matches the specified value.

src/meta/types/src/proto_display.rs

@@ -14,6 +14,8 @@
 
 use std::fmt::Display;
 use std::fmt::Formatter;
+use std::time::Duration;
+use std::time::SystemTime;
 
 use num_traits::FromPrimitive;
 
@@ -144,13 +146,13 @@ impl Display for TxnGetRequest {
 
 impl Display for TxnPutRequest {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        write!(
-            f,
-            "Put key={}, need prev_value: {}",
-            self.key, self.prev_value
-        )?;
+        write!(f, "Put key={}", self.key)?;
         if let Some(expire_at) = self.expire_at {
-            write!(f, " expire at: {}", expire_at)?;
+            let t = SystemTime::UNIX_EPOCH + Duration::from_millis(expire_at);
+            write!(f, " expire_at: {:?}", t)?;
+        }
+        if let Some(ttl_ms) = self.ttl_ms {
+            write!(f, "  ttl: {:?}", Duration::from_millis(ttl_ms))?;
         }
         Ok(())
     }