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https://issues.apache.org/jira/browse/RATIS-272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16589514#comment-16589514
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ASF GitHub Bot commented on RATIS-272:
--------------------------------------
Github user VladRodionov commented on a diff in the pull request:
https://github.com/apache/incubator-ratis/pull/4#discussion_r212153677
--- Diff:
ratis-logservice/src/main/java/org/apache/ratis/logservice/api/LogReader.java
---
@@ -0,0 +1,53 @@
+/**
+ * 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.ratis.logservice.api;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.List;
+
+/**
+ * Synchronous client interface to read from a LogStream.
+ */
+public interface LogReader extends AutoCloseable {
+
+ /**
+ * Seeks to the position before the record at the provided {@code
offset} in the LogStream.
+ *
+ * @param offset A non-negative, offset in the LogStream
+ * @return A future for when the operation is completed.
+ */
+ void seek(long recordId) throws IOException;
--- End diff --
Seeking by record id is expensive to implement. One has to support separate
index {recordid -> file offset}. This should be not ID, but generic "offset",
which maps 1 -> 1 to file offset. The only use case, where we need positional
reads (at least in logs) is to resume sequential reading from the last read
offset (HBase replication as an example).
We have to separate logs from message queues - they are totally different
by their purpose.
> Design ideal API
> ----------------
>
> Key: RATIS-272
> URL: https://issues.apache.org/jira/browse/RATIS-272
> Project: Ratis
> Issue Type: Sub-task
> Components: LogService
> Reporter: Josh Elser
> Priority: Major
>
> With influence from Apache DistributedLog, Kafka, and BookKeeper, design an
> API that balances the ideal notion of what a distribute log system should
> look like, but also considers the needs of HBase to replace a WAL.
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