History cache per partes

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

@@ -0,0 +1,91 @@
+/*
+ * 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 org.opengrok.indexer.logger.LoggerFactory;
+import org.opengrok.indexer.util.Statistics;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Helper class to split sequence of VCS changesets into number of intervals.
+ * This is then used in {@link Repository#createCache(HistoryCache, String)}
+ * to store history in chunks, for VCS repositories that support this.
+ */
+public class BoundaryChangesets {
+    private int cnt = 0;
+    private final List<String> result = new ArrayList<>();
+
+    private final int maxCount;
+    private final RepositoryWithPerPartesHistory repository;
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(BoundaryChangesets.class);
+
+    public BoundaryChangesets(RepositoryWithPerPartesHistory repository) {
+        this.repository = repository;
+        this.maxCount = repository.getPerPartesCount();
+        if (maxCount <= 1) {
+            throw new RuntimeException(String.format("per partes count for repository ''%s'' " +
+                    "must be stricly greater than 1", repository.getDirectoryName()));
+        }
+    }
+
+    private void reset() {
+        cnt = 0;
+        result.clear();
+    }
+
+    /**
+     * @param sinceRevision start revision ID
+     * @return immutable list of revision IDs denoting the intervals
+     * @throws HistoryException if there is problem traversing the changesets in the repository
+     */
+    public synchronized List<String> getBoundaryChangesetIDs(String sinceRevision) throws HistoryException {
+        reset();
+
+        LOGGER.log(Level.FINE, "getting boundary changesets for ''{0}''", repository.getDirectoryName());
+        Statistics stat = new Statistics();
+
+        repository.accept(sinceRevision, this::visit);
+
+        // The changesets need to go from oldest to newest.
+        Collections.reverse(result);
+
+        stat.report(LOGGER, Level.FINE,
+                String.format("done getting boundary changesets for ''%s'' (%d entries)",
+                        repository.getDirectoryName(), result.size()));
+
+        return List.copyOf(result);
+    }
+
+    private void visit(String id) {
+        if (cnt != 0 && cnt % maxCount == 0) {
+            result.add(id);
+        }
+        cnt++;
+    }
+}