proof of concept: split history cache generation into chunks

fixes oracle#3243

opengrok-indexer/src/main/java/org/opengrok/indexer/history/FileHistoryCache.java

@@ -150,6 +150,7 @@ private void doFileHistory(String filename, List<HistoryEntry> historyEntries,
 
         storeFile(hist, file, repository, !renamed);
 
+        // TODO: readjust for per partes history indexing
         statRepoHist.report(LOGGER, Level.FINER,
                 String.format("Done storing history cache for '%s'", filename),
                 "filehistorycache.history.store");
@@ -437,14 +438,6 @@ public void store(History history, Repository repository)
             return;
         }
 
-        LOGGER.log(Level.FINE,
-            "Storing history for repository {0}",
-            new Object[] {repository.getDirectoryName()});
-
-        // Firstly store the history for the top-level directory.
-        doFileHistory(repository.getDirectoryName(), history.getHistoryEntries(),
-                repository, env.getSourceRootFile(), null, false);
-
         HashMap<String, List<HistoryEntry>> map = new HashMap<>();
         HashMap<String, Boolean> acceptanceCache = new HashMap<>();
 
@@ -513,7 +506,8 @@ public void store(History history, Repository repository)
             fileHistoryCount++;
         }
 
-        LOGGER.log(Level.FINE, "Stored history for {0} files", fileHistoryCount);
+        LOGGER.log(Level.FINE, "Stored history for {0} files in repository ''{1}''",
+                new Object[]{fileHistoryCount, repository.getDirectoryName()});
 
         if (!handleRenamedFiles) {
             finishStore(repository, latestRev);
@@ -735,7 +729,8 @@ private String getRepositoryCachedRevPath(Repository repository) {
      * @param repository repository
      * @param rev latest revision which has been just indexed
      */
-    private void storeLatestCachedRevision(Repository repository, String rev) {
+    @Override
+    public void storeLatestCachedRevision(Repository repository, String rev) {
         Writer writer = null;
 
         try {

opengrok-indexer/src/main/java/org/opengrok/indexer/history/GitRepository.java

@@ -33,6 +33,7 @@
 import java.io.Reader;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Paths;
+import java.util.Collections;
 import java.util.Date;
 import java.util.List;
 import java.util.ArrayList;
@@ -86,6 +87,7 @@
 import org.opengrok.indexer.util.Executor;
 import org.opengrok.indexer.util.ForbiddenSymlinkException;
 import org.opengrok.indexer.util.LazilyInstantiate;
+import org.opengrok.indexer.util.Statistics;
 import org.opengrok.indexer.util.Version;
 
 import static org.opengrok.indexer.history.HistoryEntry.TAGS_SEPARATOR;
@@ -94,7 +96,7 @@
  * Access to a Git repository.
  *
  */
-public class GitRepository extends Repository {
+public class GitRepository extends RepositoryPerPartesHistory {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(GitRepository.class);
 
@@ -524,6 +526,51 @@ History getHistory(File file) throws HistoryException {
 
     @Override
     History getHistory(File file, String sinceRevision) throws HistoryException {
+        return getHistory(file, sinceRevision, null);
+    }
+
+    // TODO: add test
+    public List<String> getBoundaryChangesetIDs(String sinceRevision) throws HistoryException {
+        List<String> result = new ArrayList<>();
+        final int maxCount = 1024;  // TODO
+
+        Statistics stat = new Statistics();
+        try (org.eclipse.jgit.lib.Repository repository = getJGitRepository(getDirectoryName());
+             RevWalk walk = new RevWalk(repository)) {
+
+            if (sinceRevision != null) {
+                walk.markUninteresting(walk.lookupCommit(repository.resolve(sinceRevision)));
+            }
+            walk.markStart(walk.parseCommit(repository.resolve(Constants.HEAD)));
+
+            int cnt = 0;
+            String lastId = null;
+            for (RevCommit commit : walk) {
+                if (cnt != 0 && cnt % maxCount == 0) {
+                    // Do not abbreviate the Id as this could cause AmbiguousObjectException in getHistory().
+                    lastId = commit.getId().name();
+                    result.add(lastId);
+                }
+                cnt++;
+            }
+        } catch (IOException e) {
+            throw new HistoryException(e);
+        }
+
+        // The changesets need to go from oldest to newest.
+        Collections.reverse(result);
+
+        // Add null to finish the last step in Repository#createCache().
+        result.add(null);
+
+        stat.report(LOGGER, Level.FINE,
+                String.format("done getting boundary changesets for ''%s'' (%d entries)",
+                        getDirectoryName(), result.size()));
+
+        return result;
+    }
+
+    public History getHistory(File file, String sinceRevision, String tillRevision) throws HistoryException {
         final List<HistoryEntry> entries = new ArrayList<>();
         final List<String> renamedFiles = new ArrayList<>();
 
@@ -533,7 +580,12 @@ History getHistory(File file, String sinceRevision) throws HistoryException {
             if (sinceRevision != null) {
                 walk.markUninteresting(walk.lookupCommit(repository.resolve(sinceRevision)));
             }
-            walk.markStart(walk.parseCommit(repository.resolve(Constants.HEAD)));
+
+            if (tillRevision != null) {
+                walk.markStart(walk.lookupCommit(repository.resolve(tillRevision)));
+            } else {
+                walk.markStart(walk.parseCommit(repository.resolve(Constants.HEAD)));
+            }
 
             String relativePath = RuntimeEnvironment.getInstance().getPathRelativeToSourceRoot(file);
             if (!getDirectoryNameRelative().equals(relativePath)) {
@@ -761,6 +813,14 @@ String determineBranch(CommandTimeoutType cmdType) throws IOException {
         }
     }
 
+    // TODO: add test for this
+    public String determineCurrentVersionId() throws IOException {
+        try (org.eclipse.jgit.lib.Repository repository = getJGitRepository(getDirectoryName())) {
+            Ref head = repository.exactRef(Constants.HEAD);
+            return getCommit(repository, head).getId().abbreviate(GIT_ABBREV_LEN).name();
+        }
+    }
+
     @Override
     public String determineCurrentVersion(CommandTimeoutType cmdType) throws IOException {
         try (org.eclipse.jgit.lib.Repository repository = getJGitRepository(getDirectoryName())) {

opengrok-indexer/src/main/java/org/opengrok/indexer/history/HistoryCache.java

@@ -115,6 +115,9 @@ boolean hasCacheForDirectory(File directory, Repository repository)
     String getLatestCachedRevision(Repository repository)
             throws HistoryException;
 
+    // TODO
+    void storeLatestCachedRevision(Repository repository, String version);
+
     /**
      * Get the last modified times for all files and subdirectories in the
      * specified directory.

opengrok-indexer/src/main/java/org/opengrok/indexer/history/Repository.java

@@ -53,6 +53,7 @@
 import org.opengrok.indexer.util.Executor;
 
 import org.jetbrains.annotations.NotNull;
+import org.opengrok.indexer.util.Statistics;
 
 /**
  * An interface for an external repository.
@@ -141,8 +142,7 @@ public String getRepoCommand() {
      * @return partial history for file
      * @throws HistoryException on error accessing the history
      */
-    History getHistory(File file, String sinceRevision)
-            throws HistoryException {
+    History getHistory(File file, String sinceRevision) throws HistoryException {
 
         // If we want an incremental history update and get here, warn that
         // it may be slow.
@@ -361,17 +361,16 @@ protected String getRevisionForAnnotate(String history_revision) {
      *
      * @throws HistoryException on error
      */
-    final void createCache(HistoryCache cache, String sinceRevision)
-            throws HistoryException {
+    final void createCache(HistoryCache cache, String sinceRevision) throws HistoryException {
+
         if (!isWorking()) {
             return;
         }
 
         // If we don't have a directory parser, we can't create the cache
         // this way. Just give up and return.
         if (!hasHistoryForDirectories()) {
-            LOGGER.log(
-                    Level.INFO,
+            LOGGER.log(Level.INFO,
                     "Skipping creation of history cache for {0}, since retrieval "
                             + "of history for directories is not implemented for this "
                             + "repository type.", getDirectoryName());
@@ -381,31 +380,45 @@ final void createCache(HistoryCache cache, String sinceRevision)
         File directory = new File(getDirectoryName());
 
         History history;
-        try {
+        if (!(this instanceof RepositoryPerPartesHistory)) {
             history = getHistory(directory, sinceRevision);
-        } catch (HistoryException he) {
-            if (sinceRevision == null) {
-                // Failed to get full history, so fail.
-                throw he;
+            finishCreateCache(cache, history);
+            return;
+        }
+
+        // To avoid storing complete History memory, split the work into multiple chunks.
+        RepositoryPerPartesHistory repo = (RepositoryPerPartesHistory) this;
+        List<String> boundaryChangesets = repo.getBoundaryChangesetIDs(sinceRevision);
+        int cnt = 0;
+        for (String tillRevision: boundaryChangesets) {
+            Statistics stat = new Statistics();
+            history = repo.getHistory(directory, sinceRevision, tillRevision);
+            if (history.getHistoryEntries().size() == 0) {
+                // TODO
+                break;
             }
-            // Failed to get partial history. This may have been caused
-            // by changes in the revision numbers since the last update
-            // (bug #14724) so we'll try to regenerate the cache from
-            // scratch instead.
-            LOGGER.log(Level.WARNING,
-                    "Failed to get partial history. Attempting to "
-                    + "recreate the history cache from scratch.", he);
-            history = null;
+
+            finishCreateCache(cache, history);
+            sinceRevision = tillRevision;
+
+            stat.report(LOGGER, Level.FINE, String.format("finished chunk %d/%d of history cache for repository ''%s''",
+                    ++cnt, boundaryChangesets.size(), this.getDirectoryName()));
         }
 
-        if (sinceRevision != null && history == null) {
-            // Failed to get partial history, now get full history instead.
-            history = getHistory(directory);
-            // Got full history successfully. Clear the history cache so that
-            // we can recreate it from scratch.
-            cache.clear(this);
+        /*
+         * Need to reset the latest cachedRevision as the last finishCreateCache() above
+         * wrote the changeset ID of the last part.
+         * TODO: probably not necessary now ?
+         */
+        try {
+            // TODO: does not work well if finishStore() failed
+            cache.storeLatestCachedRevision(this, repo.determineCurrentVersionId());
+        } catch (IOException e) {
+            throw new HistoryException(e);
         }
+    }
 
+    private void finishCreateCache(HistoryCache cache, History history) throws HistoryException {
         // We need to refresh list of tags for incremental reindex.
         RuntimeEnvironment env = RuntimeEnvironment.getInstance();
         if (env.isTagsEnabled() && this.hasFileBasedTags()) {

opengrok-indexer/src/main/java/org/opengrok/indexer/history/RepositoryPerPartesHistory.java

@@ -0,0 +1,37 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * See LICENSE.txt included in this distribution for the specific
+ * language governing permissions and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at LICENSE.txt.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ */
+package org.opengrok.indexer.history;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+
+public abstract class RepositoryPerPartesHistory extends Repository {
+    private static final long serialVersionUID = -3433255821312805064L;
+
+    abstract History getHistory(File directory, String sinceRevision, String tillRevision) throws HistoryException;
+
+    abstract List<String> getBoundaryChangesetIDs(String sinceRevision) throws HistoryException;
+
+    abstract String determineCurrentVersionId() throws IOException;
+}

opengrok-indexer/src/test/java/org/opengrok/indexer/history/FileHistoryCacheTest.java

@@ -30,6 +30,7 @@
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.opengrok.indexer.condition.RepositoryInstalled.Type.GIT;
 import static org.opengrok.indexer.condition.RepositoryInstalled.Type.MERCURIAL;
 import static org.opengrok.indexer.condition.RepositoryInstalled.Type.SCCS;
 import static org.opengrok.indexer.condition.RepositoryInstalled.Type.SUBVERSION;
@@ -247,6 +248,24 @@ public void testStoreAndGetIncrementalTags() throws Exception {
                 retrievedUpdatedHistoryMainC.getHistoryEntries(), false);
     }
 
+    /**
+     * TODO
+     * move this to RepositoryTest ?
+     */
+    @Test
+    @EnabledOnOs({OS.LINUX, OS.MAC, OS.SOLARIS, OS.AIX, OS.OTHER})
+    @EnabledForRepository(GIT)
+    public void testIncrementalStore() throws Exception {
+        File reposRoot = new File(repositories.getSourceRoot(), "git");
+
+        Repository repo = RepositoryFactory.getRepository(reposRoot);
+        History historyToStore = repo.getHistory(reposRoot);
+
+        repo.createCache(cache, null);
+
+        // TODO
+    }
+
     /**
      * Basic tests for the {@code store()} and {@code get()} methods.
      */