[opt](rowcount) refresh external table's rowcount async (#32997)

In previous implementation, the row count cache will be expired after 10min(by default),
and after expiration, the next row count request will miss the cache, causing unstable query plan.

In this PR, the cache will be refreshed after Config.external_cache_expire_time_minutes_after_access,
so that the cache entry will remain fresh.

fe/fe-core/src/main/java/org/apache/doris/datasource/ExternalMetaCacheMgr.java

@@ -71,7 +71,8 @@ public class ExternalMetaCacheMgr {
                 "ExternalMetaCacheMgr", 120, true);
         hudiPartitionMgr = HudiPartitionMgr.get(executor);
         fsCache = new FileSystemCache(executor);
-        rowCountCache = new ExternalRowCountCache(executor);
+        rowCountCache = new ExternalRowCountCache(executor,
+                Config.external_cache_expire_time_minutes_after_access * 60, null);
         icebergMetadataCacheMgr = new IcebergMetadataCacheMgr();
         maxComputeMetadataCacheMgr = new MaxComputeMetadataCacheMgr();
     }

fe/fe-core/src/main/java/org/apache/doris/datasource/ExternalRowCountCache.java

@@ -24,6 +24,7 @@ import org.apache.doris.statistics.util.StatisticsUtil;
 
 import com.github.benmanes.caffeine.cache.AsyncLoadingCache;
 import com.github.benmanes.caffeine.cache.Caffeine;
+import lombok.Getter;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
@@ -37,14 +38,19 @@ public class ExternalRowCountCache {
     private static final Logger LOG = LogManager.getLogger(ExternalRowCountCache.class);
     private final AsyncLoadingCache<RowCountKey, Optional<Long>> rowCountCache;
 
-    public ExternalRowCountCache(ExecutorService executor) {
+    public ExternalRowCountCache(ExecutorService executor, long refreshAfterWriteSeconds,
+            BasicAsyncCacheLoader<RowCountKey, Optional<Long>> loader) {
+        // 1. set expireAfterWrite to 1 day, avoid too many entries
+        // 2. set refreshAfterWrite to 10min(default), so that the cache will be refreshed after 10min
         rowCountCache = Caffeine.newBuilder()
                 .maximumSize(Config.max_external_table_row_count_cache_num)
-                .expireAfterWrite(Duration.ofMinutes(Config.external_cache_expire_time_minutes_after_access))
+                .expireAfterAccess(Duration.ofDays(1))
+                .refreshAfterWrite(Duration.ofSeconds(refreshAfterWriteSeconds))
                 .executor(executor)
-                .buildAsync(new RowCountCacheLoader());
+                .buildAsync(loader == null ? new RowCountCacheLoader() : loader);
     }
 
+    @Getter
     public static class RowCountKey {
         private final long catalogId;
         private final long dbId;
@@ -74,7 +80,6 @@ public class ExternalRowCountCache {
     }
 
     public static class RowCountCacheLoader extends BasicAsyncCacheLoader<RowCountKey, Optional<Long>> {
-
         @Override
         protected Optional<Long> doLoad(RowCountKey rowCountKey) {
             try {

fe/fe-core/src/test/java/org/apache/doris/datasource/ExternalRowCountCacheTest.java

@@ -0,0 +1,100 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.apache.doris.datasource;
+
+import org.apache.doris.datasource.ExternalRowCountCache.RowCountKey;
+import org.apache.doris.statistics.BasicAsyncCacheLoader;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class ExternalRowCountCacheTest {
+    private ExternalRowCountCache cache;
+    private ExecutorService executorService;
+
+    public static class TestLoader extends BasicAsyncCacheLoader<RowCountKey, Optional<Long>> {
+
+        private AtomicLong incr = new AtomicLong(333);
+
+        @Override
+        protected Optional<Long> doLoad(RowCountKey rowCountKey) {
+            if (rowCountKey.getTableId() == 1) {
+                return Optional.of(111L);
+            } else if (rowCountKey.getTableId() == 2) {
+                return Optional.of(222L);
+            } else if (rowCountKey.getTableId() == 3) {
+                try {
+                    Thread.sleep(1000);
+                } catch (InterruptedException e) {
+                    throw new RuntimeException(e);
+                }
+                System.out.println("load: " + incr.get());
+                return Optional.of(incr.incrementAndGet());
+            }
+            return Optional.empty();
+        }
+    }
+
+    @BeforeEach
+    public void setUp() {
+        executorService = Executors.newFixedThreadPool(2);
+        cache = new ExternalRowCountCache(executorService, 2, new TestLoader());
+    }
+
+    @Test
+    public void test() throws Exception {
+        // table 1
+        long rowCount = cache.getCachedRowCount(1, 1, 1);
+        Assertions.assertEquals(0, rowCount);
+        Thread.sleep(1000);
+        rowCount = cache.getCachedRowCount(1, 1, 1);
+        Assertions.assertEquals(111, rowCount);
+
+        // table 2
+        rowCount = cache.getCachedRowCount(1, 1, 2);
+        Assertions.assertEquals(0, rowCount);
+        Thread.sleep(1000);
+        rowCount = cache.getCachedRowCount(1, 1, 2);
+        Assertions.assertEquals(222, rowCount);
+
+        // table 3
+        rowCount = cache.getCachedRowCount(1, 1, 3);
+        // first get, it should be 0 because the loader is async
+        Assertions.assertEquals(0, rowCount);
+        // After sleep 2 sec and then get, it should be 1
+        Thread.sleep(2000);
+        rowCount = cache.getCachedRowCount(1, 1, 3);
+        Assertions.assertEquals(334, rowCount);
+        // sleep 3 sec to trigger refresh
+        Thread.sleep(3000);
+        rowCount = cache.getCachedRowCount(1, 1, 3);
+        // the refresh will be triggered only when query it, so it should still be 1
+        Assertions.assertEquals(334, rowCount);
+        // sleep 2 sec to wait for the doLoad
+        Thread.sleep(2000);
+        rowCount = cache.getCachedRowCount(1, 1, 3);
+        // refresh done, value should be 2
+        Assertions.assertEquals(335, rowCount);
+    }
+}