refactor: one place modify

Signed-off-by: discord9 <discord9@163.com>

src/query/src/dummy_catalog.rs

@@ -329,20 +329,25 @@ fn scan_request_from_query_context(
     query_ctx: &QueryContext,
 ) -> Result<ScanRequest> {
     let decision = decide_flow_scan(query_ctx, region_id)?;
-    let mut scan_request = build_scan_request(query_ctx, region_id, &decision);
-    apply_cached_snapshot(query_ctx, region_id, &decision, &mut scan_request);
-
-    Ok(scan_request)
+    Ok(build_scan_request(query_ctx, region_id, &decision))
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct FlowScanDecision {
     /// Whether this region is the flow sink-table scan.
+    /// Sink scans intentionally bypass incremental and snapshot-binding semantics.
     is_sink_scan: bool,
-    /// Whether this region should bind a snapshot upper bound on scan open.
+    /// Whether this scan should bind a memtable upper bound when opening the scan.
+    /// This is only the initial intent; if a cached bound already exists in `query_ctx`,
+    /// we reuse that cached bound instead and clear this flag.
     snapshot_on_scan: bool,
-    /// Optional lower exclusive memtable sequence bound.
+    /// Optional lower exclusive memtable sequence bound for incremental reads.
+    /// When set, only rows with sequence strictly greater than this bound are read from memtables.
     memtable_min_sequence: Option<u64>,
+    /// Optional cached per-region snapshot already bound in `query_ctx`.
+    /// When present, this becomes the effective memtable upper bound and suppresses
+    /// binding a new snapshot on scan open.
+    memtable_max_sequence: Option<u64>,
 }
 
 impl FlowScanDecision {
@@ -351,6 +356,7 @@ impl FlowScanDecision {
             is_sink_scan: true,
             snapshot_on_scan: false,
             memtable_min_sequence: None,
+            memtable_max_sequence: None,
         }
     }
 }
@@ -358,16 +364,20 @@ impl FlowScanDecision {
 fn decide_flow_scan(query_ctx: &QueryContext, region_id: RegionId) -> Result<FlowScanDecision> {
     let flow_extensions = FlowQueryExtensions::from_extensions(&query_ctx.extensions())?;
 
-    // Fast path for normal queries: no flow-related scan context at all.
+    // Fast path for normal queries: no flow-related scan context at all, so keep
+    // the request as a plain scan and avoid any flow-specific decision making.
     if !flow_extensions.has_flow_context() {
         return Ok(FlowScanDecision {
             is_sink_scan: false,
             snapshot_on_scan: false,
             memtable_min_sequence: None,
+            memtable_max_sequence: query_ctx.get_snapshot(region_id.as_u64()),
         });
     }
 
-    // Sink-table scans intentionally bypass all flow scan semantics.
+    // Sink-table scans intentionally bypass all flow scan semantics. They should
+    // behave like plain reads and must not participate in incremental lower bounds
+    // or per-region snapshot binding/reuse.
     if flow_extensions.sink_table_id == Some(region_id.table_id()) {
         return Ok(FlowScanDecision::plain_scan());
     }
@@ -384,10 +394,14 @@ fn decide_flow_scan(query_ctx: &QueryContext, region_id: RegionId) -> Result<Flo
         None
     };
 
+    let memtable_max_sequence = query_ctx.get_snapshot(region_id.as_u64());
+
     Ok(FlowScanDecision {
         is_sink_scan: false,
-        snapshot_on_scan: flow_extensions.should_collect_region_watermark(),
+        snapshot_on_scan: memtable_max_sequence.is_none()
+            && flow_extensions.should_collect_region_watermark(),
         memtable_min_sequence,
+        memtable_max_sequence,
     })
 }
 
@@ -396,33 +410,28 @@ fn build_scan_request(
     region_id: RegionId,
     decision: &FlowScanDecision,
 ) -> ScanRequest {
+    // Build the initial scan request from the final decision known at provider creation
+    // time. A later scan may still refresh `memtable_max_sequence` if another source scan
+    // has bound a snapshot into `query_ctx` after this provider was created.
     ScanRequest {
         sst_min_sequence: query_ctx.sst_min_sequence(region_id.as_u64()),
         snapshot_on_scan: decision.snapshot_on_scan,
         memtable_min_sequence: decision.memtable_min_sequence,
+        memtable_max_sequence: decision.memtable_max_sequence,
         ..Default::default()
     }
 }
 
-fn apply_cached_snapshot(
-    query_ctx: &QueryContext,
-    region_id: RegionId,
-    decision: &FlowScanDecision,
-    scan_request: &mut ScanRequest,
-) {
-    if decision.is_sink_scan {
-        return;
-    }
-
-    apply_cached_snapshot_to_request(query_ctx, region_id, scan_request);
-}
-
 fn apply_cached_snapshot_to_request(
     query_ctx: &QueryContext,
     region_id: RegionId,
     scan_request: &mut ScanRequest,
 ) {
     if let Some(snapshot_sequence) = query_ctx.get_snapshot(region_id.as_u64()) {
+        // Reuse the previously bound per-region snapshot instead of rebinding a new
+        // upper bound on scan open. This refresh is still needed at scan time because
+        // the provider's cached request may have been built before another source scan
+        // bound the shared query-level snapshot into `query_ctx`.
         scan_request.memtable_max_sequence = Some(snapshot_sequence);
         scan_request.snapshot_on_scan = false;
     }