Transaction reads should not interfere with add/update/delete (#3163)

andreachild · web-flow · commit db369864ab77 · 2025-07-25T12:38:45.000-07:00
https://issues.apache.org/jira/browse/TINKERPOP-3142 Changed TinkerElementContainer to no longer consider element reads as being 'used in a transaction' which should be reserved for element add/update/delete only. This is appropriate for TinkerTransactionGraph because the isolation level is 'read committed'. With this isolation level, we do not need to protect against 'unrepeatable reads' or 'phantom reads'. Prior to this change, a read-only thread could cause a 'Conflict: element modified in another transaction' error in a separate thread which was attempting add/drop/update.
diff --git a/CHANGELOG.asciidoc b/CHANGELOG.asciidoc
@@ -57,6 +57,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 * Increased default `max_content_length`/`max_msg_size` in `gremlin-python` from 4MB to 10MB.
 * Added the `PopContaining` interface designed to get label and `Pop` combinations held in a `PopInstruction` object.
 * Fixed bug preventing a vertex from being dropped and then re-added in the same `TinkerTransaction`
+* Fixed bug which could cause a 'Conflict: element modified in another transaction' when a transaction is attempting to add/drop/update a vertex or edge while another transaction is reading the same vertex or edge.
 
 [[release-3-7-3]]
 === TinkerPop 3.7.3 (October 23, 2024)
diff --git a/docs/src/reference/implementations-tinkergraph.asciidoc b/docs/src/reference/implementations-tinkergraph.asciidoc
@@ -221,8 +221,8 @@ supported. You can think of the transaction as belonging to a thread, any traver
 will share the same transaction even if you attempt to start a new transaction.
 
 `TinkerTransactionGraph` provides the `read committed` transaction isolation level. This means that it will always try to
-guard against dirty reads. While you may notice stricter isolation semantics in some cases, you should not depend on
-this behavior as it may change in the future.
+guard against dirty reads but will not prevent non-repeatable reads or phantom reads. While you may notice stricter 
+isolation semantics in some cases, you should not depend on this behavior as it may change in the future.
 
 `TinkerTransactionGraph` employs optimistic locking as its locking strategy. This reduces complexity in the design as
 there are fewer timeouts that the user needs to manage. However, a consequence of this approach is that a transaction
diff --git a/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerElementContainer.java b/tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerElementContainer.java
@@ -59,7 +59,7 @@ final class TinkerElementContainer<T extends TinkerElement> {
     private final ThreadLocal<Boolean> isReadInTx = ThreadLocal.withInitial(() -> false);
 
     /**
-     * Count of usages of container in different transactions.
+     * Count of modification/deletion/addition usages of container in different transactions (reads do not contribute to this count).
      * Needed to understand whether this element is used in other transactions or it can be deleted during rollback.
      */
     private final AtomicInteger usesInTransactions = new AtomicInteger(0);
@@ -97,7 +97,6 @@ public T getWithClone(final TinkerTransaction tx) {
 
         if (!isReadInTx.get()) {
             isReadInTx.set(true);
-            usesInTransactions.incrementAndGet();
             tx.markRead(this);
         }
 
@@ -205,7 +204,7 @@ public boolean updatedOutsideTransaction() {
     }
 
     /**
-     * Used to understand if element is in use by any transaction.
+     * Used to understand if element is in use (added, modified, or deleted) by any transaction.
      */
     public boolean inUse() {
         return usesInTransactions.get() > 0;
@@ -246,8 +245,6 @@ private void updateUsesCount() {
             usesInTransactions.decrementAndGet();
         if (isModifiedInTx.get())
             usesInTransactions.decrementAndGet();
-        if (isReadInTx.get())
-            usesInTransactions.decrementAndGet();
     }
 
     /**
diff --git a/tinkergraph-gremlin/src/test/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerTransactionGraphTest.java b/tinkergraph-gremlin/src/test/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerTransactionGraphTest.java
