fix(core): fix non-partition table truncate not working correctly alter table add column

core/src/main/java/io/questdb/cairo/ColumnVersionWriter.java

@@ -35,10 +35,10 @@
 public class ColumnVersionWriter extends ColumnVersionReader {
     private final CairoConfiguration configuration;
     private final MemoryCMARW mem;
+    private final boolean partitioned;
     private boolean hasChanges;
     private long size;
     private long version;
-    private final boolean partitioned;
 
 
     // size should be read from the transaction file
@@ -133,20 +133,38 @@ public void removePartition(long partitionTimestamp) {
     }
 
     public void truncate() {
-        if (cachedColumnVersionList.size() > 0 && partitioned) {
+        if (cachedColumnVersionList.size() > 0) {
+
             final long defaultPartitionTimestamp = COL_TOP_DEFAULT_PARTITION;
             int from = cachedColumnVersionList.binarySearchBlock(BLOCK_SIZE_MSB, defaultPartitionTimestamp + 1, BinarySearch.SCAN_UP);
             if (from < 0) {
                 from = -from - 1;
             }
-            // Remove all partitions after COL_TOP_DEFAULT_PARTITION
-            if (from < cachedColumnVersionList.size()) {
-                cachedColumnVersionList.setPos(from);
-            }
-            // Keep default column version but reset the added timestamp to min
-            for (int i = 0, n = cachedColumnVersionList.size(); i < n; i += BLOCK_SIZE) {
-                cachedColumnVersionList.setQuick(i + TIMESTAMP_ADDED_PARTITION_OFFSET, defaultPartitionTimestamp);
+
+            if (partitioned) {
+                // Remove all partitions after COL_TOP_DEFAULT_PARTITION
+                if (from < cachedColumnVersionList.size()) {
+                    cachedColumnVersionList.setPos(from);
+                }
+                // Keep default column version but reset the added timestamp to min
+                for (int i = 0, n = cachedColumnVersionList.size(); i < n; i += BLOCK_SIZE) {
+                    cachedColumnVersionList.setQuick(i + TIMESTAMP_ADDED_PARTITION_OFFSET, defaultPartitionTimestamp);
+                }
+            } else {
+                // We have to keep all the column name txns because the files are truncated but not re-created.
+                // But we want to remove all the column tops.
+                // The column name txn can be added when the column is added via alter table or when column is updated.
+                // When ALTER table add column is executed it creates a record in the NaN partition with the column name txn
+                // and a record in 0 (default) partition with the column top.
+                // When the column is changed using UPDATE SQL, the column name txn is only set in 0 (default) partition.
+                // These 2 scenarios are test covered in TruncateTest.
+
+                // Result action is to remove all column tops and keep all column name txns.
+                for (int i = from; i < cachedColumnVersionList.size(); i += BLOCK_SIZE) {
+                    cachedColumnVersionList.setQuick(i + COLUMN_TOP_OFFSET, 0);
+                }
             }
+
             hasChanges = true;
             commit();
         }

core/src/test/java/io/questdb/test/griffin/SqlCompilerImplTest.java

@@ -5228,6 +5228,8 @@ public void testSelectCharInNull() throws Exception {
     @Test
     public void testSelectConcurrentDDL() throws Exception {
 
+        // On Windows CI this test can fail with Metadata read timeout with small timeout.
+        node1.getConfigurationOverrides().setSpinLockTimeout(30000);
         ddl("create table x (a int, b int, c int)");
 
         final AtomicBoolean ddlError = new AtomicBoolean(false);

core/src/test/java/io/questdb/test/griffin/TruncateTest.java

@@ -44,6 +44,49 @@
 
 public class TruncateTest extends AbstractCairoTest {
 
+    @Test
+    public void testAddColumnTruncate() throws Exception {
+        assertMemoryLeak(() -> {
+            ddl(
+                    "create table y as (" +
+                            "select timestamp_sequence(0, 1000000000) timestamp," +
+                            " x " +
+                            " from long_sequence(10)" +
+                            ") timestamp (timestamp)"
+            );
+
+
+            ddl("alter table y add column new_x int", sqlExecutionContext);
+            ddl("truncate table y");
+
+            insert("insert into y values('2022-02-24', 1, 2)");
+
+            assertSql("timestamp\tx\tnew_x\n" +
+                    "2022-02-24T00:00:00.000000Z\t1\t2\n", "select * from y");
+        });
+    }
+
+    @Test
+    public void testUpdateThenTruncate() throws Exception {
+        assertMemoryLeak(() -> {
+            ddl(
+                    "create table y as (" +
+                            "select timestamp_sequence(0, 1000000000) timestamp," +
+                            " x " +
+                            " from long_sequence(10)" +
+                            ") timestamp (timestamp)"
+            );
+
+            update("update y set x = 10");
+            ddl("truncate table y");
+
+            insert("insert into y values('2022-02-24', 1)");
+
+            assertSql("timestamp\tx\n" +
+                    "2022-02-24T00:00:00.000000Z\t1\n", "select * from y");
+        });
+    }
+
     @Test
     public void testDropColumnTruncatePartitionByNone() throws Exception {
         assertMemoryLeak(() -> {