[core] Share JDBC connection pool across catalog instances in same JVM

paimon-common/src/main/java/org/apache/paimon/client/ClientPool.java

@@ -68,7 +68,12 @@ public <R> R run(Action<R, C, E> action) throws E, InterruptedException {
                     client = ensureActiveClient(client);
                     return action.run(client);
                 } finally {
+                    // Return client to the deque, then check if close() raced us.
+                    // The deque's lock ensures either drainTo or remove sees the client.
                     clients.addFirst(client);
+                    if (this.clients == null && clients.remove(client)) {
+                        close(client);
+                    }
                 }
             }
         }

paimon-core/src/main/java/org/apache/paimon/jdbc/CachedJdbcClientPool.java

@@ -0,0 +1,118 @@
+/*
+ * 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.paimon.jdbc;
+
+import org.apache.paimon.annotation.VisibleForTesting;
+import org.apache.paimon.options.Options;
+
+import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import static org.apache.paimon.options.CatalogOptions.CLIENT_POOL_SIZE;
+import static org.apache.paimon.options.CatalogOptions.URI;
+
+/**
+ * A cache that shares {@link JdbcClientPool} instances across multiple catalog instances in the
+ * same JVM. This prevents each Flink operator from creating its own connection pool when using the
+ * JDBC catalog.
+ *
+ * <p>The cache is keyed by JDBC URI and catalog key. Pools live for the lifetime of the JVM and are
+ * closed via a shutdown hook.
+ */
+public class CachedJdbcClientPool {
+
+    private static final ConcurrentMap<Key, JdbcClientPool> CLIENT_POOLS =
+            new ConcurrentHashMap<>();
+
+    static {
+        Runtime.getRuntime()
+                .addShutdownHook(
+                        new Thread(
+                                () -> {
+                                    for (JdbcClientPool pool : CLIENT_POOLS.values()) {
+                                        pool.close();
+                                    }
+                                    CLIENT_POOLS.clear();
+                                },
+                                "jdbc-client-pool-shutdown"));
+    }
+
+    private final Key key;
+    private final int poolSize;
+    private final String dbUrl;
+    private final Map<String, String> props;
+
+    public CachedJdbcClientPool(Options options, Map<String, String> props) {
+        this.dbUrl = options.get(URI);
+        this.poolSize = options.get(CLIENT_POOL_SIZE);
+        this.props = props;
+        this.key = Key.of(dbUrl, options.get(JdbcCatalogOptions.CATALOG_KEY));
+    }
+
+    /** Returns the shared {@link JdbcClientPool} for this cache key, creating one if needed. */
+    public JdbcClientPool get() {
+        return CLIENT_POOLS.computeIfAbsent(key, k -> new JdbcClientPool(poolSize, dbUrl, props));
+    }
+
+    @VisibleForTesting
+    static ConcurrentMap<Key, JdbcClientPool> clientPools() {
+        return CLIENT_POOLS;
+    }
+
+    @VisibleForTesting
+    static void resetCache() {
+        for (JdbcClientPool pool : CLIENT_POOLS.values()) {
+            pool.close();
+        }
+        CLIENT_POOLS.clear();
+    }
+
+    static class Key {
+        private final String uri;
+        private final String catalogKey;
+
+        private Key(String uri, String catalogKey) {
+            this.uri = uri;
+            this.catalogKey = catalogKey;
+        }
+
+        static Key of(String uri, String catalogKey) {
+            return new Key(uri, catalogKey);
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            Key that = (Key) o;
+            return Objects.equals(uri, that.uri) && Objects.equals(catalogKey, that.catalogKey);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(uri, catalogKey);
+        }
+    }
+}

paimon-core/src/main/java/org/apache/paimon/jdbc/JdbcCatalog.java

@@ -98,11 +98,7 @@ protected JdbcCatalog(
         this.options = context.options();
         this.warehouse = warehouse;
         Preconditions.checkNotNull(options, "Invalid catalog properties: null");
-        this.connections =
-                new JdbcClientPool(
-                        options.get(CatalogOptions.CLIENT_POOL_SIZE),
-                        options.get(CatalogOptions.URI.key()),
-                        options.toMap());
+        this.connections = new CachedJdbcClientPool(options, options.toMap()).get();
         try {
             initializeCatalogTablesIfNeed();
         } catch (SQLException e) {
@@ -569,7 +565,8 @@ public void repairTable(Identifier identifier) throws TableNotExistException {
 
     @Override
     public void close() throws Exception {
-        connections.close();
+        // Do not close the connection pool here — it is shared across catalog instances
+        // via CachedJdbcClientPool and will be evicted/closed by the cache when idle.
     }
 
     private boolean syncTableProperties() {

paimon-core/src/main/java/org/apache/paimon/jdbc/JdbcCatalogLockContext.java

@@ -19,7 +19,6 @@
 package org.apache.paimon.jdbc;
 
 import org.apache.paimon.catalog.CatalogLockContext;
-import org.apache.paimon.options.CatalogOptions;
 import org.apache.paimon.options.Options;
 
 /** Jdbc lock context. */
@@ -41,11 +40,7 @@ public Options options() {
 
     public JdbcClientPool connections() {
         if (connections == null) {
-            connections =
-                    new JdbcClientPool(
-                            options.get(CatalogOptions.CLIENT_POOL_SIZE),
-                            options.get(CatalogOptions.URI.key()),
-                            options.toMap());
+            connections = new CachedJdbcClientPool(options, options.toMap()).get();
         }
         return connections;
     }

paimon-core/src/test/java/org/apache/paimon/jdbc/CachedJdbcClientPoolTest.java

@@ -0,0 +1,131 @@
+/*
+ * 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.paimon.jdbc;
+
+import org.apache.paimon.options.CatalogOptions;
+import org.apache.paimon.options.Options;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import java.sql.SQLException;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/** Tests for {@link CachedJdbcClientPool}. */
+public class CachedJdbcClientPoolTest {
+
+    @AfterEach
+    void tearDown() {
+        CachedJdbcClientPool.resetCache();
+    }
+
+    @Test
+    void testSameKeyReturnsSamePool() {
+        String uri = sqliteUri();
+        Options options = createOptions(uri, "my-catalog");
+
+        CachedJdbcClientPool cache1 = new CachedJdbcClientPool(options, options.toMap());
+        CachedJdbcClientPool cache2 = new CachedJdbcClientPool(options, options.toMap());
+
+        assertThat(cache1.get()).isSameAs(cache2.get());
+    }
+
+    @Test
+    void testDifferentUriReturnsDifferentPool() {
+        Options options1 = createOptions(sqliteUri(), "my-catalog");
+        Options options2 = createOptions(sqliteUri(), "my-catalog");
+
+        CachedJdbcClientPool cache1 = new CachedJdbcClientPool(options1, options1.toMap());
+        CachedJdbcClientPool cache2 = new CachedJdbcClientPool(options2, options2.toMap());
+
+        assertThat(cache1.get()).isNotSameAs(cache2.get());
+    }
+
+    @Test
+    void testDifferentCatalogKeyReturnsDifferentPool() {
+        String uri = sqliteUri();
+        Options options1 = createOptions(uri, "catalog-a");
+        Options options2 = createOptions(uri, "catalog-b");
+
+        CachedJdbcClientPool cache1 = new CachedJdbcClientPool(options1, options1.toMap());
+        CachedJdbcClientPool cache2 = new CachedJdbcClientPool(options2, options2.toMap());
+
+        assertThat(cache1.get()).isNotSameAs(cache2.get());
+    }
+
+    @Test
+    void testPoolIsUsable() throws SQLException, InterruptedException {
+        Options options = createOptions(sqliteUri(), "test-catalog");
+        CachedJdbcClientPool cache = new CachedJdbcClientPool(options, options.toMap());
+
+        JdbcClientPool pool = cache.get();
+        Boolean result = pool.run(conn -> !conn.isClosed());
+
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    void testMultipleCatalogInstancesSharePool() {
+        String uri = sqliteUri();
+        Options options = createOptions(uri, "shared-catalog");
+
+        JdbcCatalog catalog1 =
+                new JdbcCatalog(
+                        new org.apache.paimon.fs.local.LocalFileIO(),
+                        "shared-catalog",
+                        org.apache.paimon.catalog.CatalogContext.create(options),
+                        "/tmp/warehouse1");
+        JdbcCatalog catalog2 =
+                new JdbcCatalog(
+                        new org.apache.paimon.fs.local.LocalFileIO(),
+                        "shared-catalog",
+                        org.apache.paimon.catalog.CatalogContext.create(options),
+                        "/tmp/warehouse2");
+
+        assertThat(catalog1.getConnections()).isSameAs(catalog2.getConnections());
+    }
+
+    @Test
+    void testResetCacheClearsAllPools() {
+        Options options = createOptions(sqliteUri(), "test-catalog");
+        CachedJdbcClientPool cache = new CachedJdbcClientPool(options, options.toMap());
+        JdbcClientPool pool = cache.get();
+
+        assertThat(pool).isNotNull();
+        assertThat(CachedJdbcClientPool.clientPools()).isNotEmpty();
+
+        CachedJdbcClientPool.resetCache();
+
+        assertThat(CachedJdbcClientPool.clientPools()).isEmpty();
+    }
+
+    private static Options createOptions(String uri, String catalogKey) {
+        Options options = new Options();
+        options.set(CatalogOptions.URI, uri);
+        options.set(JdbcCatalogOptions.CATALOG_KEY, catalogKey);
+        options.set(CatalogOptions.CLIENT_POOL_SIZE, 2);
+        return options;
+    }
+
+    private static String sqliteUri() {
+        return "jdbc:sqlite:file::memory:?ic" + UUID.randomUUID().toString().replace("-", "");
+    }
+}