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Posted to commits@pulsar.apache.org by GitBox <gi...@apache.org> on 2021/11/12 19:30:09 UTC
[GitHub] [pulsar] merlimat commented on a change in pull request #12776: [metadata] Add RocksdbMetadataStore
merlimat commented on a change in pull request #12776:
URL: https://github.com/apache/pulsar/pull/12776#discussion_r748510190
##########
File path: pulsar-metadata/src/main/java/org/apache/pulsar/metadata/api/Notification.java
##########
@@ -19,8 +19,10 @@
package org.apache.pulsar.metadata.api;
import lombok.Data;
+import lombok.EqualsAndHashCode;
@Data
+@EqualsAndHashCode
Review comment:
nit: `@Data` already implies `@EqualsAndHashCode`: https://projectlombok.org/features/Data
##########
File path: pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/RocksdbMetadataStore.java
##########
@@ -0,0 +1,428 @@
+/**
+ * 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.pulsar.metadata.impl;
+
+import com.google.common.annotations.VisibleForTesting;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumSet;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.metadata.api.GetResult;
+import org.apache.pulsar.metadata.api.MetadataStoreConfig;
+import org.apache.pulsar.metadata.api.MetadataStoreException;
+import org.apache.pulsar.metadata.api.Notification;
+import org.apache.pulsar.metadata.api.NotificationType;
+import org.apache.pulsar.metadata.api.Stat;
+import org.apache.pulsar.metadata.api.extended.CreateOption;
+import org.rocksdb.InfoLogLevel;
+import org.rocksdb.Options;
+import org.rocksdb.ReadOptions;
+import org.rocksdb.RocksDB;
+import org.rocksdb.RocksDBException;
+import org.rocksdb.RocksIterator;
+import org.rocksdb.Transaction;
+import org.rocksdb.TransactionDB;
+import org.rocksdb.TransactionDBOptions;
+import org.rocksdb.WriteBatch;
+import org.rocksdb.WriteOptions;
+
+/**
+ *
+ */
+@Slf4j
+public class RocksdbMetadataStore extends AbstractMetadataStore {
+ private static final byte[] SEQUENTIAL_ID_KEY = toBytes("__metadata_sequentialId_key");
+ private static final byte[] INSTANCE_ID_KEY = toBytes("__metadata_instanceId_key");
+
+ private final long instanceId;
+ private final AtomicLong sequentialIdGenerator;
+
+ private final TransactionDB db;
+
+ private final WriteOptions optionSync;
+ private final WriteOptions optionDontSync;
+
+ private final ReadOptions optionCache;
+ private final ReadOptions optionDontCache;
+
+ private final WriteBatch emptyBatch;
+
+ @Data
+ @AllArgsConstructor
+ @NoArgsConstructor
+ private static class MetaValue {
+ private static final int HEADER_SIZE = 8 + 8 + 8 + 8 + 1;
+
+ long version;
+ long owner;
+ long createdTimestamp;
+ long modifiedTimestamp;
+ boolean ephemeral;
+ byte[] data;
+
+ public byte[] serialize() {
+ byte[] result = new byte[HEADER_SIZE + data.length];
+ ByteBuffer buffer = ByteBuffer.wrap(result);
+ buffer.putLong(version);
+ buffer.putLong(owner);
+ buffer.putLong(createdTimestamp);
+ buffer.putLong(modifiedTimestamp);
+ buffer.put((byte) (ephemeral ? 1 : 0));
+ buffer.put(data);
+ return result;
+ }
+
+ public static MetaValue parse(byte[] dataBytes) throws MetadataStoreException {
+ if (dataBytes == null) {
+ return null;
+ }
+ if (dataBytes.length < HEADER_SIZE) {
+ throw new MetadataStoreException("Invalid MetaValue data");
+ }
+ ByteBuffer buffer = ByteBuffer.wrap(dataBytes);
+ MetaValue metaValue = new MetaValue();
+ metaValue.version = buffer.getLong();
+ metaValue.owner = buffer.getLong();
+ metaValue.createdTimestamp = buffer.getLong();
+ metaValue.modifiedTimestamp = buffer.getLong();
+ metaValue.ephemeral = buffer.get() > 0;
+ metaValue.data = new byte[buffer.remaining()];
+ buffer.get(metaValue.data);
+ return metaValue;
+ }
+ }
+
+ @VisibleForTesting
+ static byte[] toBytes(String s) {
+ return s.getBytes(StandardCharsets.UTF_8);
+ }
+
+ @VisibleForTesting
+ static String toString(byte[] bytes) {
+ return new String(bytes, StandardCharsets.UTF_8);
+ }
+
+ @VisibleForTesting
+ static byte[] toBytes(long value) {
+ return ByteBuffer.wrap(new byte[8]).putLong(value).array();
+ }
+
+ @VisibleForTesting
+ static long toLong(byte[] bytes) {
+ return ByteBuffer.wrap(bytes).getLong();
+ }
+
+ /**
+ * @param metadataURL format "rocksdb://{storePath}"
+ * @param metadataStoreConfig
+ * @throws MetadataStoreException
+ */
+ public RocksdbMetadataStore(String metadataURL, MetadataStoreConfig metadataStoreConfig)
+ throws MetadataStoreException {
+ try {
+ RocksDB.loadLibrary();
+ } catch (Throwable t) {
+ throw new MetadataStoreException("Failed to load RocksDB JNI library", t);
+ }
+
+ this.optionSync = new WriteOptions();
+ this.optionDontSync = new WriteOptions();
+ this.optionCache = new ReadOptions();
+ this.optionDontCache = new ReadOptions();
+ this.emptyBatch = new WriteBatch();
+
+ try (Options options = new Options()) {
+ options.setCreateIfMissing(true);
Review comment:
We should take a Rocksdb config file path argument from our config, so that a user will be able to control all the aspects of RocksDB.
##########
File path: pulsar-metadata/src/test/java/org/apache/pulsar/metadata/impl/RocksdbMetadataStoreTest.java
##########
@@ -0,0 +1,186 @@
+/**
+ * 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.pulsar.metadata.impl;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.EnumSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.ExecutionException;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.io.FileUtils;
+import org.apache.pulsar.metadata.api.GetResult;
+import org.apache.pulsar.metadata.api.MetadataStore;
+import org.apache.pulsar.metadata.api.MetadataStoreConfig;
+import org.apache.pulsar.metadata.api.MetadataStoreException;
+import org.apache.pulsar.metadata.api.MetadataStoreFactory;
+import org.apache.pulsar.metadata.api.Notification;
+import org.apache.pulsar.metadata.api.NotificationType;
+import org.apache.pulsar.metadata.api.Stat;
+import org.apache.pulsar.metadata.api.extended.CreateOption;
+import org.apache.pulsar.metadata.api.extended.MetadataStoreExtended;
+import org.assertj.core.util.Lists;
+import org.awaitility.Awaitility;
+import org.testng.Assert;
+import org.testng.annotations.AfterClass;
+import org.testng.annotations.BeforeClass;
+import org.testng.annotations.Test;
+
+@Slf4j
+public class RocksdbMetadataStoreTest {
+
+ private static MetadataStore store;
+ private static Path tempDir;
+
+
+ @BeforeClass
+ public static void beforeClass() throws Exception {
+ tempDir = Files.createTempDirectory("RocksdbMetadataStoreTest");
+ log.info("Temp dir:{}", tempDir.toAbsolutePath());
+ store = MetadataStoreFactory.create("rocksdb://" + tempDir.toAbsolutePath(),
+ MetadataStoreConfig.builder().build());
+ Assert.assertTrue(store instanceof RocksdbMetadataStore);
+ }
+
+ @AfterClass
+ public static void afterClass() throws Exception {
+ store.close();
+ FileUtils.deleteQuietly(tempDir.toFile());
+ }
+
+ @Test
+ public void testConvert() {
+ String s = "testConvert";
+ Assert.assertEquals(s, RocksdbMetadataStore.toString(RocksdbMetadataStore.toBytes(s)));
+
+ long l = 12345;
+ Assert.assertEquals(l, RocksdbMetadataStore.toLong(RocksdbMetadataStore.toBytes(l)));
+ }
+
+ @Test
+ public void testMetadataStore() throws Exception {
Review comment:
Would it make sense to run these tests on all the other implementations as well, in order to ensure consistent behavior?
##########
File path: pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/RocksdbMetadataStore.java
##########
@@ -0,0 +1,428 @@
+/**
+ * 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.pulsar.metadata.impl;
+
+import com.google.common.annotations.VisibleForTesting;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumSet;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.metadata.api.GetResult;
+import org.apache.pulsar.metadata.api.MetadataStoreConfig;
+import org.apache.pulsar.metadata.api.MetadataStoreException;
+import org.apache.pulsar.metadata.api.Notification;
+import org.apache.pulsar.metadata.api.NotificationType;
+import org.apache.pulsar.metadata.api.Stat;
+import org.apache.pulsar.metadata.api.extended.CreateOption;
+import org.rocksdb.InfoLogLevel;
+import org.rocksdb.Options;
+import org.rocksdb.ReadOptions;
+import org.rocksdb.RocksDB;
+import org.rocksdb.RocksDBException;
+import org.rocksdb.RocksIterator;
+import org.rocksdb.Transaction;
+import org.rocksdb.TransactionDB;
+import org.rocksdb.TransactionDBOptions;
+import org.rocksdb.WriteBatch;
+import org.rocksdb.WriteOptions;
+
+/**
+ *
+ */
+@Slf4j
+public class RocksdbMetadataStore extends AbstractMetadataStore {
+ private static final byte[] SEQUENTIAL_ID_KEY = toBytes("__metadata_sequentialId_key");
+ private static final byte[] INSTANCE_ID_KEY = toBytes("__metadata_instanceId_key");
+
+ private final long instanceId;
+ private final AtomicLong sequentialIdGenerator;
+
+ private final TransactionDB db;
+
+ private final WriteOptions optionSync;
+ private final WriteOptions optionDontSync;
+
+ private final ReadOptions optionCache;
+ private final ReadOptions optionDontCache;
+
+ private final WriteBatch emptyBatch;
+
+ @Data
+ @AllArgsConstructor
+ @NoArgsConstructor
+ private static class MetaValue {
+ private static final int HEADER_SIZE = 8 + 8 + 8 + 8 + 1;
+
+ long version;
+ long owner;
+ long createdTimestamp;
+ long modifiedTimestamp;
+ boolean ephemeral;
+ byte[] data;
+
+ public byte[] serialize() {
+ byte[] result = new byte[HEADER_SIZE + data.length];
+ ByteBuffer buffer = ByteBuffer.wrap(result);
+ buffer.putLong(version);
+ buffer.putLong(owner);
+ buffer.putLong(createdTimestamp);
+ buffer.putLong(modifiedTimestamp);
+ buffer.put((byte) (ephemeral ? 1 : 0));
+ buffer.put(data);
+ return result;
Review comment:
Since this is not going to change very often, I agree we don't need to use Protobuf or similar, though we should leave the door open for future modifications.
I would add:
* `size` field as the first field
* `format-version` identifier to understand which format was used for a given value
* Add a note that we can only add new fields, but not change or remove existing fields
* When deserializing, stop reading at the current known HEADER size, ignoring newer unknown fields.
##########
File path: pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/RocksdbMetadataStore.java
##########
@@ -0,0 +1,428 @@
+/**
+ * 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.pulsar.metadata.impl;
+
+import com.google.common.annotations.VisibleForTesting;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumSet;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.metadata.api.GetResult;
+import org.apache.pulsar.metadata.api.MetadataStoreConfig;
+import org.apache.pulsar.metadata.api.MetadataStoreException;
+import org.apache.pulsar.metadata.api.Notification;
+import org.apache.pulsar.metadata.api.NotificationType;
+import org.apache.pulsar.metadata.api.Stat;
+import org.apache.pulsar.metadata.api.extended.CreateOption;
+import org.rocksdb.InfoLogLevel;
+import org.rocksdb.Options;
+import org.rocksdb.ReadOptions;
+import org.rocksdb.RocksDB;
+import org.rocksdb.RocksDBException;
+import org.rocksdb.RocksIterator;
+import org.rocksdb.Transaction;
+import org.rocksdb.TransactionDB;
+import org.rocksdb.TransactionDBOptions;
+import org.rocksdb.WriteBatch;
+import org.rocksdb.WriteOptions;
+
+/**
+ *
+ */
+@Slf4j
+public class RocksdbMetadataStore extends AbstractMetadataStore {
+ private static final byte[] SEQUENTIAL_ID_KEY = toBytes("__metadata_sequentialId_key");
+ private static final byte[] INSTANCE_ID_KEY = toBytes("__metadata_instanceId_key");
+
+ private final long instanceId;
+ private final AtomicLong sequentialIdGenerator;
+
+ private final TransactionDB db;
+
+ private final WriteOptions optionSync;
+ private final WriteOptions optionDontSync;
+
+ private final ReadOptions optionCache;
+ private final ReadOptions optionDontCache;
+
+ private final WriteBatch emptyBatch;
+
+ @Data
+ @AllArgsConstructor
+ @NoArgsConstructor
+ private static class MetaValue {
+ private static final int HEADER_SIZE = 8 + 8 + 8 + 8 + 1;
+
+ long version;
+ long owner;
+ long createdTimestamp;
+ long modifiedTimestamp;
+ boolean ephemeral;
+ byte[] data;
+
+ public byte[] serialize() {
+ byte[] result = new byte[HEADER_SIZE + data.length];
+ ByteBuffer buffer = ByteBuffer.wrap(result);
+ buffer.putLong(version);
+ buffer.putLong(owner);
+ buffer.putLong(createdTimestamp);
+ buffer.putLong(modifiedTimestamp);
+ buffer.put((byte) (ephemeral ? 1 : 0));
+ buffer.put(data);
+ return result;
+ }
+
+ public static MetaValue parse(byte[] dataBytes) throws MetadataStoreException {
+ if (dataBytes == null) {
+ return null;
+ }
+ if (dataBytes.length < HEADER_SIZE) {
+ throw new MetadataStoreException("Invalid MetaValue data");
+ }
+ ByteBuffer buffer = ByteBuffer.wrap(dataBytes);
+ MetaValue metaValue = new MetaValue();
+ metaValue.version = buffer.getLong();
+ metaValue.owner = buffer.getLong();
+ metaValue.createdTimestamp = buffer.getLong();
+ metaValue.modifiedTimestamp = buffer.getLong();
+ metaValue.ephemeral = buffer.get() > 0;
+ metaValue.data = new byte[buffer.remaining()];
+ buffer.get(metaValue.data);
+ return metaValue;
+ }
+ }
+
+ @VisibleForTesting
+ static byte[] toBytes(String s) {
+ return s.getBytes(StandardCharsets.UTF_8);
+ }
+
+ @VisibleForTesting
+ static String toString(byte[] bytes) {
+ return new String(bytes, StandardCharsets.UTF_8);
+ }
+
+ @VisibleForTesting
+ static byte[] toBytes(long value) {
+ return ByteBuffer.wrap(new byte[8]).putLong(value).array();
+ }
+
+ @VisibleForTesting
+ static long toLong(byte[] bytes) {
+ return ByteBuffer.wrap(bytes).getLong();
+ }
+
+ /**
+ * @param metadataURL format "rocksdb://{storePath}"
+ * @param metadataStoreConfig
+ * @throws MetadataStoreException
+ */
+ public RocksdbMetadataStore(String metadataURL, MetadataStoreConfig metadataStoreConfig)
+ throws MetadataStoreException {
+ try {
+ RocksDB.loadLibrary();
+ } catch (Throwable t) {
+ throw new MetadataStoreException("Failed to load RocksDB JNI library", t);
+ }
+
+ this.optionSync = new WriteOptions();
+ this.optionDontSync = new WriteOptions();
+ this.optionCache = new ReadOptions();
+ this.optionDontCache = new ReadOptions();
+ this.emptyBatch = new WriteBatch();
+
+ try (Options options = new Options()) {
+ options.setCreateIfMissing(true);
+
+ String dataDir = metadataURL.substring("rocksdb://".length());
+ Path dataPath = FileSystems.getDefault().getPath(dataDir);
+ Files.createDirectories(dataPath);
+ configLog(options);
+ TransactionDBOptions transactionDBOptions = new TransactionDBOptions();
+ db = TransactionDB.open(options, transactionDBOptions, dataPath.toString());
+
+ sequentialIdGenerator = new AtomicLong(0);
+ byte[] value = db.get(SEQUENTIAL_ID_KEY);
+ if (value != null) {
+ sequentialIdGenerator.set(toLong(value));
+ } else {
+ db.put(INSTANCE_ID_KEY, toBytes(sequentialIdGenerator.get()));
+ }
+
+ value = db.get(INSTANCE_ID_KEY);
+ if (value != null) {
+ instanceId = toLong(value) + 1;
+ } else {
+ instanceId = 0;
+ }
+ db.put(INSTANCE_ID_KEY, toBytes(instanceId));
+
+
+ } catch (RocksDBException e) {
+ throw new MetadataStoreException("Error open RocksDB database", e);
+ } catch (MetadataStoreException e) {
+ throw e;
+ } catch (Throwable t) {
+ throw new MetadataStoreException(t);
+ }
+
+ optionSync.setSync(true);
+ optionDontSync.setSync(false);
+
+ optionCache.setFillCache(true);
+ optionDontCache.setFillCache(false);
+ }
+
+ private void configLog(Options options) throws IOException {
+ // Configure file path
+ String logPath = System.getProperty("pulsar.log.dir", "");
+ Path logPathSetting;
+ if (!logPath.isEmpty()) {
+ logPathSetting = FileSystems.getDefault().getPath(logPath + "/rocksdb-log");
+ Files.createDirectories(logPathSetting);
+ options.setDbLogDir(logPathSetting.toString());
+ }
+
+ // Configure log level
+ String logLevel = System.getProperty("pulsar.log.level", "info");
+ switch (logLevel) {
+ case "debug":
+ options.setInfoLogLevel(InfoLogLevel.DEBUG_LEVEL);
+ break;
+ case "info":
+ options.setInfoLogLevel(InfoLogLevel.INFO_LEVEL);
+ break;
+ case "warn":
+ options.setInfoLogLevel(InfoLogLevel.WARN_LEVEL);
+ break;
+ case "error":
+ options.setInfoLogLevel(InfoLogLevel.ERROR_LEVEL);
+ break;
+ default:
+ log.warn("Unrecognized RockDB log level: {}", logLevel);
+ }
+
+ // Keep log files for 1month
+ options.setKeepLogFileNum(30);
+ options.setLogFileTimeToRoll(TimeUnit.DAYS.toSeconds(1));
+ }
+
+ @Override
+ public void close() throws Exception {
+ db.close();
+ optionSync.close();
+ optionDontSync.close();
+ optionCache.close();
+ optionDontCache.close();
+ emptyBatch.close();
+ super.close();
+ }
+
+ @Override
+ public CompletableFuture<Optional<GetResult>> get(String path) {
+ if (path.isEmpty()) {
Review comment:
Maybe these checks could be done in the `AbstractMetadataStore`
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