[BACKPORT 2024.1][#8096] YSQL: Fix flaky test TestPgDdlConcurrency#te…

…stModifiedTableWrite

Summary:
The test is runs a DDL thread concurrently with 10 DML threads in ASAN/TSAN
builds and 50 DML threads in other builds. With 50 threads it still takes too
much resources, with 10 threads it is more flaky.

This diff makes two changes:
(1) Use 10 DML threads for all builds to reduce test resources.
(2) Changed the test to run until one of the expected errors appear to make it
more reliable.
Jira: DB-4809

Original commit: e9311b4 / D40929

Test Plan:
On AlmaLinux:
./yb_build.sh release --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1
./yb_build.sh asan --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1
./yb_build.sh tsan --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1
./yb_build.sh debug --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1
./yb_build.sh fastdebug --gcc11 --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1

On MacOS:
./yb_build.sh release --java-test 'org.yb.pgsql.TestPgDdlConcurrency#testModifiedTableWrite' -n 100 --tp 1

Reviewers: hsunder

Reviewed By: hsunder

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D40989

java/yb-pgsql/src/test/java/org/yb/pgsql/TestPgDdlConcurrency.java

@@ -39,7 +39,8 @@ protected int getInitialNumTServers() {
   public void testModifiedTableWrite() throws Exception {
     try (Statement stmt = connection.createStatement()) {
       stmt.execute("CREATE TABLE t(k INT PRIMARY KEY, v1 INT DEFAULT 10, v2 INT DEFAULT 20)");
-      int count = 50;
+      final int count = 10;
+
       final AtomicBoolean errorsDetected = new AtomicBoolean(false);
       final AtomicBoolean stopped = new AtomicBoolean(false);
       final CyclicBarrier barrier = new CyclicBarrier(count);
@@ -50,9 +51,10 @@ public void testModifiedTableWrite() throws Exception {
         b.withTServer(count % miniCluster.getNumTServers());
         connections[i] = b.connect();
       }
+      final AtomicInteger expectedExceptionsCount = new AtomicInteger(0);
       threads[0] = new Thread(() -> {
         try (Statement lstmt = connections[0].createStatement()) {
-          while (!stopped.get() && !errorsDetected.get()) {
+          while (!stopped.get() && !errorsDetected.get() && expectedExceptionsCount.get() == 0) {
             barrier.await();
             lstmt.execute("ALTER TABLE t DROP COLUMN IF EXISTS v");
             lstmt.execute("ALTER TABLE t ADD COLUMN v INT DEFAULT 100");
@@ -67,13 +69,12 @@ public void testModifiedTableWrite() throws Exception {
           barrier.reset();
         }
       });
-      final AtomicInteger expectedExceptionsCount = new AtomicInteger(0);
       for (int i = 1; i < count; ++i) {
         final int idx = i;
         threads[i] = new Thread(() -> {
           try (Statement lstmt = connections[idx].createStatement()) {
             for (int item_idx = 0;
-                 !stopped.get() && !errorsDetected.get() && item_idx < 1000000;
+                 !stopped.get() && !errorsDetected.get() && expectedExceptionsCount.get() == 0;
                  item_idx += 2) {
               barrier.await();
               try {
@@ -108,8 +109,7 @@ public void testModifiedTableWrite() throws Exception {
         });
       }
       Arrays.stream(threads).forEach(t -> t.start());
-      final long startTimeMs = System.currentTimeMillis();
-      while (System.currentTimeMillis() - startTimeMs < 10000 && !errorsDetected.get()) {
+      while (!errorsDetected.get() && expectedExceptionsCount.get() == 0) {
         Thread.sleep(1000);
       }
       stopped.set(true);