Merge pull request #1146 from pantonov/tt-genid

Added TransactionalTree::generate_id()

src/context.rs

@@ -122,7 +122,8 @@ impl Context {
     /// a blocking flush to fsync the latest counter, ensuring
     /// that we will never give out the same counter twice.
     pub fn generate_id(&self) -> Result<u64> {
-        self.pagecache.generate_id()
+        let _cc = concurrency_control::read();
+        self.pagecache.generate_id_inner()
     }
 
     pub(crate) fn pin_log(&self, guard: &Guard) -> Result<RecoveryGuard<'_>> {

src/pagecache/mod.rs

@@ -1793,8 +1793,7 @@ impl PageCache {
     /// previous persisted counter wasn't synced to disk yet, we will do
     /// a blocking flush to fsync the latest counter, ensuring
     /// that we will never give out the same counter twice.
-    pub(crate) fn generate_id(&self) -> Result<u64> {
-        let _cc = concurrency_control::read();
+    pub(crate) fn generate_id_inner(&self) -> Result<u64> {
         let ret = self.idgen.fetch_add(1, Release);
 
         trace!("generating ID {}", ret);

src/transaction.rs

@@ -335,6 +335,20 @@ impl TransactionalTree {
         *self.flush_on_commit.borrow_mut() = true;
     }
 
+    /// Generate a monotonic ID. Not guaranteed to be
+    /// contiguous or idempotent, can produce different values in the
+    /// same transaction in case of conflicts.
+    /// Written to disk every `idgen_persist_interval`
+    /// operations, followed by a blocking flush. During recovery, we
+    /// take the last recovered generated ID and add 2x
+    /// the `idgen_persist_interval` to it. While persisting, if the
+    /// previous persisted counter wasn't synced to disk yet, we will do
+    /// a blocking flush to fsync the latest counter, ensuring
+    /// that we will never give out the same counter twice.
+    pub fn generate_id(&self) -> Result<u64> {
+        self.tree.context.pagecache.generate_id_inner()
+    }
+
     fn unstage(&self) {
         unimplemented!()
     }