io.permazen.kv.raft.fallback.OverwriteMergeStrategy Maven / Gradle / Ivy

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/*
 * Copyright (C) 2015 Archie L. Cobbs. All rights reserved.
 */

package io.permazen.kv.raft.fallback;

import io.permazen.kv.KVPair;
import io.permazen.kv.KVTransaction;
import io.permazen.util.CloseableIterator;

import java.util.Date;

/**
 * {@link MergeStrategy} that completely overwrites the destination database with the content of the source database.
 */
public class OverwriteMergeStrategy implements MergeStrategy {

    @Override
    public void mergeAndCommit(KVTransaction src, KVTransaction dst, Date lastActiveTime) {
        this.overwrite(src, dst);
        src.commit();
        dst.commit();
    }

    /**
     * Overwrite one key/value database with another.
     *
     * 
     * This method deletes every key/value pair in {@code dst}, and then copy every key/value pair
     * in {@code src} into {@code dst}.
     *
     * 
     * Does not commit {@code src} or {@code dst}.
     *
     * @param src database to copy from
     * @param dst database to copy {@code src} onto
     */
    protected void overwrite(KVTransaction src, KVTransaction dst) {
        dst.removeRange(null, null);
        try (CloseableIterator i = src.getRange(null, null)) {
            while (i.hasNext()) {
                final KVPair pair = i.next();
                dst.put(pair.getKey(), pair.getValue());
            }
        }
    }

    @Override
    public String toString() {
        return "Overwrite";
    }
}