[Kernel] Use SLF4J for logging in kernel-api

build.sbt

@@ -222,11 +222,13 @@ lazy val kernelApi = (project in file("kernel/kernel-api"))
     Test / javaOptions ++= Seq("-ea"),
     libraryDependencies ++= Seq(
       "org.roaringbitmap" % "RoaringBitmap" % "0.9.25",
+      "org.slf4j" % "slf4j-api" % "2.0.9",
 
       "com.fasterxml.jackson.core" % "jackson-databind" % "2.13.5" % "test",
       "org.scalatest" %% "scalatest" % scalaTestVersion % "test",
       "junit" % "junit" % "4.13" % "test",
-      "com.novocode" % "junit-interface" % "0.11" % "test"
+      "com.novocode" % "junit-interface" % "0.11" % "test",
+      "org.slf4j" % "slf4j-log4j12" % "2.0.9" % "test"
     ),
     javaCheckstyleSettings("kernel/dev/checkstyle.xml"),
     // Unidoc settings
@@ -251,7 +253,8 @@ lazy val kernelDefaults = (project in file("kernel/kernel-defaults"))
       "org.scalatest" %% "scalatest" % scalaTestVersion % "test",
       "junit" % "junit" % "4.13" % "test",
       "commons-io" % "commons-io" % "2.8.0" % "test",
-      "com.novocode" % "junit-interface" % "0.11" % "test"
+      "com.novocode" % "junit-interface" % "0.11" % "test",
+      "org.slf4j" % "slf4j-log4j12" % "2.0.9" % "test"
     ),
     javaCheckstyleSettings("kernel/dev/checkstyle.xml"),
       // Unidoc settings

kernel/kernel-api/src/main/java/io/delta/kernel/internal/TableImpl.java

@@ -25,9 +25,8 @@
 
 import io.delta.kernel.internal.fs.Path;
 import io.delta.kernel.internal.snapshot.SnapshotManager;
-import io.delta.kernel.internal.util.Logging;
 
-public class TableImpl implements Table, Logging {
+public class TableImpl implements Table {
     public static Table forPath(TableClient tableClient, String path)
         throws TableNotFoundException {
         // Resolve the path to fully qualified table path using the `TableClient` APIs

kernel/kernel-api/src/main/java/io/delta/kernel/internal/replay/LogReplay.java

@@ -36,7 +36,6 @@
 import io.delta.kernel.internal.fs.Path;
 import io.delta.kernel.internal.lang.Lazy;
 import io.delta.kernel.internal.snapshot.LogSegment;
-import io.delta.kernel.internal.util.Logging;
 import io.delta.kernel.internal.util.Tuple2;
 
 /**
@@ -56,7 +55,7 @@
  * - {@link #getAddFilesAsColumnarBatches}: return all active (not tombstoned) AddFiles as
  *                                          {@link ColumnarBatch}s
  */
-public class LogReplay implements Logging {
+public class LogReplay {
 
     /** Read schema when searching for the latest Protocol and Metadata. */
     public static final StructType PROTOCOL_METADATA_READ_SCHEMA = new StructType()

kernel/kernel-api/src/main/java/io/delta/kernel/internal/snapshot/SnapshotManager.java

@@ -22,6 +22,9 @@
 import java.util.stream.Collectors;
 import java.util.stream.LongStream;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import io.delta.kernel.Snapshot;
 import io.delta.kernel.TableNotFoundException;
 import io.delta.kernel.client.TableClient;
@@ -35,15 +38,15 @@
 import io.delta.kernel.internal.fs.Path;
 import io.delta.kernel.internal.lang.ListUtils;
 import io.delta.kernel.internal.util.FileNames;
-import io.delta.kernel.internal.util.Logging;
 import io.delta.kernel.internal.util.Tuple2;
 import static io.delta.kernel.internal.fs.Path.getName;
 import static io.delta.kernel.internal.util.Preconditions.checkArgument;
 
-public class SnapshotManager
-    implements Logging {
+public class SnapshotManager {
     public SnapshotManager() {}
 
+    private static final Logger logger = LoggerFactory.getLogger(SnapshotManager.class);
+
     /**
      * - Verify the versions are contiguous.
      * - Verify the versions start with `expectedStartVersion` if it's specified.
@@ -98,7 +101,7 @@ private CloseableIterator<FileStatus> listFrom(
         TableClient tableClient,
         long startVersion)
         throws IOException {
-        logDebug(String.format("startVersion: %s", startVersion));
+        logger.debug("startVersion: {}", startVersion);
         return tableClient
             .getFileSystemClient()
             .listFrom(FileNames.listingPrefix(logPath, startVersion));
@@ -158,7 +161,7 @@ protected final Optional<List<FileStatus>> listDeltaAndCheckpointFiles(
         TableClient tableClient,
         long startVersion,
         Optional<Long> versionToLoad) {
-        logDebug(String.format("startVersion: %s, versionToLoad: %s", startVersion, versionToLoad));
+        logger.debug("startVersion: {}, versionToLoad: {}", startVersion, versionToLoad);
 
         return listFromOrNone(
             logPath,
@@ -225,9 +228,9 @@ private SnapshotImpl createSnapshot(
         TableClient tableClient) {
         final String startingFromStr = initSegment
             .checkpointVersionOpt
-            .map(v -> String.format(" starting from checkpoint version %s.", v))
+            .map(v -> String.format("starting from checkpoint version %s.", v))
             .orElse(".");
-        logInfo(() -> String.format("Loading version %s%s", initSegment.version, startingFromStr));
+        logger.info("Loading version {} {}", initSegment.version, startingFromStr);
 
         return new SnapshotImpl(
             logPath,
@@ -324,13 +327,13 @@ protected Optional<LogSegment> getLogSegmentForVersion(
             // recursive call to [[getLogSegmentForVersion]] below (same as before the refactor).
             newFiles = Collections.emptyList();
         }
-        logDebug(() ->
+        logger.atDebug().setMessage(() ->
             String.format(
                 "newFiles: %s",
                 Arrays.toString(newFiles.stream()
                     .map(x -> new Path(x.getPath()).getName()).toArray())
             )
-        );
+        ).log();
 
         if (newFiles.isEmpty() && !startCheckpointOpt.isPresent()) {
             // We can't construct a snapshot because the directory contained no usable commit
@@ -356,31 +359,32 @@ protected Optional<LogSegment> getLogSegmentForVersion(
         final List<FileStatus> checkpoints = checkpointsAndDeltas._1;
         final List<FileStatus> deltas = checkpointsAndDeltas._2;
 
-        logDebug(() ->
+        logger.atDebug().setMessage(() ->
             String.format(
                 "\ncheckpoints: %s\ndeltas: %s",
                 Arrays.toString(checkpoints.stream().map(
                     x -> new Path(x.getPath()).getName()).toArray()),
                 Arrays.toString(deltas.stream().map(
                     x -> new Path(x.getPath()).getName()).toArray())
             )
-        );
+        ).log();
 
         // Find the latest checkpoint in the listing that is not older than the versionToLoad
         final CheckpointInstance maxCheckpoint = versionToLoadOpt.map(CheckpointInstance::new)
             .orElse(CheckpointInstance.MAX_VALUE);
-        logDebug(String.format("lastCheckpoint: %s", maxCheckpoint));
+        logger.debug("lastCheckpoint: {}", maxCheckpoint);
 
         final List<CheckpointInstance> checkpointFiles = checkpoints
             .stream()
             .map(f -> new CheckpointInstance(f.getPath()))
             .collect(Collectors.toList());
-        logDebug(() ->
-            String.format("checkpointFiles: %s", Arrays.toString(checkpointFiles.toArray())));
+        logger.atDebug().setMessage(() ->
+            String.format("checkpointFiles: %s", Arrays.toString(checkpointFiles.toArray()))
+        ).log();
 
         final Optional<CheckpointInstance> newCheckpointOpt =
             Checkpointer.getLatestCompleteCheckpointFromList(checkpointFiles, maxCheckpoint);
-        logDebug(String.format("newCheckpointOpt: %s", newCheckpointOpt));
+        logger.debug("newCheckpointOpt: {}", newCheckpointOpt);
 
         final long newCheckpointVersion = newCheckpointOpt
             .map(c -> c.version)
@@ -415,7 +419,7 @@ protected Optional<LogSegment> getLogSegmentForVersion(
 
                 return -1L;
             });
-        logDebug(String.format("newCheckpointVersion: %s", newCheckpointVersion));
+        logger.debug("newCheckpointVersion: {}", newCheckpointVersion);
 
         // TODO: we can calculate deltasAfterCheckpoint and deltaVersions more efficiently
         // If there is a new checkpoint, start new lineage there. If `newCheckpointVersion` is -1,
@@ -427,23 +431,24 @@ protected Optional<LogSegment> getLogSegmentForVersion(
                     new Path(fileStatus.getPath())) > newCheckpointVersion)
             .collect(Collectors.toList());
 
-        logDebug(() ->
+        logger.atDebug().setMessage(() ->
             String.format(
                 "deltasAfterCheckpoint: %s",
                 Arrays.toString(deltasAfterCheckpoint.stream().map(
                     x -> new Path(x.getPath()).getName()).toArray())
             )
-        );
+        ).log();
 
         // todo again naming confusing (specify after checkpoint?)
         final LinkedList<Long> deltaVersionsAfterCheckpoint = deltasAfterCheckpoint
             .stream()
             .map(fileStatus -> FileNames.deltaVersion(new Path(fileStatus.getPath())))
             .collect(Collectors.toCollection(LinkedList::new));
 
-        logDebug(() ->
+        logger.atDebug().setMessage(() ->
             String.format("deltaVersions: %s",
-                Arrays.toString(deltaVersionsAfterCheckpoint.toArray())));
+                Arrays.toString(deltaVersionsAfterCheckpoint.toArray()))
+        ).log();
 
         // We may just be getting a checkpoint file after the filtering
         if (!deltaVersionsAfterCheckpoint.isEmpty()) {

kernel/kernel-api/src/test/resources/log4j.properties

@@ -0,0 +1,44 @@
+#
+#  Copyright (2023) The Delta Lake Project Authors.
+#  Licensed 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.
+#
+#
+# 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.
+
+# Set everything to be logged to the file target/unit-tests.log
+test.appender=file
+log4j.rootCategory=info, ${test.appender}
+log4j.appender.file=org.apache.log4j.FileAppender
+log4j.appender.file.append=true
+log4j.appender.file.file=target/unit-tests.log
+log4j.appender.file.layout=org.apache.log4j.PatternLayout
+log4j.appender.file.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss.SSS} %t %p %c{1}: %m%n
+
+# Tests that launch java subprocesses can set the "test.appender" system property to
+# "console" to avoid having the child process's logs overwrite the unit test's
+# log file.
+log4j.appender.console=org.apache.log4j.ConsoleAppender
+log4j.appender.console.target=System.err
+log4j.appender.console.layout=org.apache.log4j.PatternLayout
+log4j.appender.console.layout.ConversionPattern=%t: %m%n

kernel/kernel-defaults/src/test/resources/log4j.properties

@@ -0,0 +1,44 @@
+#
+#  Copyright (2023) The Delta Lake Project Authors.
+#  Licensed 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.
+#
+#
+# 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.
+
+# Set everything to be logged to the file target/unit-tests.log
+test.appender=file
+log4j.rootCategory=info, ${test.appender}
+log4j.appender.file=org.apache.log4j.FileAppender
+log4j.appender.file.append=true
+log4j.appender.file.file=target/unit-tests.log
+log4j.appender.file.layout=org.apache.log4j.PatternLayout
+log4j.appender.file.layout.ConversionPattern=%d{yy/MM/dd HH:mm:ss.SSS} %t %p %c{1}: %m%n
+
+# Tests that launch java subprocesses can set the "test.appender" system property to
+# "console" to avoid having the child process's logs overwrite the unit test's
+# log file.
+log4j.appender.console=org.apache.log4j.ConsoleAppender
+log4j.appender.console.target=System.err
+log4j.appender.console.layout=org.apache.log4j.PatternLayout
+log4j.appender.console.layout.ConversionPattern=%t: %m%n