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From afine <...@git.apache.org>
Subject [GitHub] zookeeper pull request #419: ZOOKEEPER-2849: Exponential back-off retry for ...
Date Thu, 16 Nov 2017 22:51:54 GMT
Github user afine commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/419#discussion_r151553425
  
    --- Diff: src/java/main/org/apache/zookeeper/server/quorum/ExponentialBackoffStrategy.java
---
    @@ -0,0 +1,192 @@
    +package org.apache.zookeeper.server.quorum;
    +
    +/**
    + * A {@link BackoffStrategy} that increases the wait time between each
    + * interval up to the configured maximum wait time.
    + */
    +public class ExponentialBackoffStrategy implements BackoffStrategy {
    +
    +    // Sensible default values to use if not set by the user
    +    private static final long DEFAULT_INITIAL_BACKOFF_MILLIS = 500L;  // 0.5s
    +    private static final long DEFAULT_MAX_BACKOFF_MILLIS = 30_000L;  // 30s
    +    private static final long DEFAULT_MAX_ELAPSED_MILLIS = 5 * 60_000L; // 10m
    +    private static final double DEFAULT_BACKOFF_MULTIPLE = 1.5;
    +
    +    // internal values per instance
    +    private final long initialBackoffMillis;
    +    private final long maxBackoffMillis;
    +    private final long maxElapsedMillis;
    +    private final double backoffMultiple;
    +
    +    // internal state
    +    private long nextWait;
    +    private long totalElapsed;
    +    private final boolean limitBackoffMillis;
    +    private final boolean checkElapsedTime;
    +
    +    /**
    +     * Construct a new instance.
    +     * @param builder the Builder to use for configuring this BackoffStrategy
    +     */
    +    private ExponentialBackoffStrategy(Builder builder) {
    +        this.initialBackoffMillis = builder.initialBackoffMillis;
    +        this.maxBackoffMillis = builder.maxBackoffMillis;
    +        this.maxElapsedMillis = builder.maxElapsedMillis;
    +        this.backoffMultiple = builder.backoffMultiple;
    +
    +        if(maxBackoffMillis == -1) {
    +            limitBackoffMillis = false;
    +        } else {
    +            limitBackoffMillis = true;
    +        }
    +
    +        if(maxElapsedMillis == -1) {
    +            checkElapsedTime = false;
    +        } else {
    +            checkElapsedTime = true;
    +        }
    +
    +        reset();
    +    }
    +
    +
    +    @Override
    +    public long nextWaitMillis() throws IllegalStateException {
    +        // check if we have exceeded the allowed maximum elapsed time
    +        if(checkElapsedTime && totalElapsed > maxElapsedMillis) {
    +            return BackoffStrategy.STOP;
    +        }
    +
    +        long waitMillis = nextWait;
    +
    +        // calculate the next wait milliseconds
    +        nextWait = Math.round(nextWait * backoffMultiple);
    +
    +        // don't exceed the allowed maximum wait milliseconds
    +        // if a maximum was configured
    +        if(limitBackoffMillis && nextWait > maxBackoffMillis) {
    +            nextWait = maxBackoffMillis;
    +        }
    +
    +        // track total elapsed time, even if we don't wait we have to assume
    +        // that some amount of time passed outside of the wait or we'll never
    +        // hit the elapsed time limit
    +        totalElapsed += waitMillis != 0 ? waitMillis : 1L;
    +        return waitMillis;
    +    }
    +
    +    @Override
    +    public void reset() {
    +        nextWait = this.initialBackoffMillis;
    +        totalElapsed = 0;
    +    }
    +
    +    /**
    +     *
    +     * @return a new {@link Builder} instance.
    +     */
    +    public static Builder builder() {
    +        return new Builder();
    +    }
    +
    +    /**
    +     * Builder for instances of {@link ExponentialBackoffStrategy}.
    +     */
    +    public static final class Builder {
    --- End diff --
    
    I'm not sure a builder is the best way to handle this. Since I think it would be nice
to have much of this be user configurable, perhaps we can just pull the config from system
properties?


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