Fix for #88021 high GC pressure when driver configured with serversid…

[johnou]

…eprepared statements.

While profiling our application I found high GC pressure coming from the mysql driver [1]. The issue arises when the driver is configured to use serverside prepared statements and the driver recreates the cache key for every query (sb.toString() invoking Arrays.copyOfRange) [2].

[1]

Stack Trace    TLABs    Total TLAB Size(bytes)    Pressure(%)
com.mysql.jdbc.ConnectionImpl.makePreparedStatementCacheKey(String, String)    16,810    1,519,493,352

[2]

private String makePreparedStatementCacheKey(String catalog, String query) {
    StringBuilder key = new StringBuilder();
    key.append("/*").append(catalog).append("*/");
    key.append(query);
    return key.toString();
}

[johnou]

Here is the benchmark code I used to verify increased throughput with the improved CompoundCacheKey (removed string concat from the constructor) vs the String key constructed with a StringBuilder.

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;

/**
 * @author Johno Crawford (johno.crawford@gmail.com)
 */
@State(Scope.Thread)
@Fork(5)
public class AllocationTest {

    private String makePreparedStatementCacheKey(String catalog, String query) {
        StringBuilder key = new StringBuilder();
        key.append("/*").append(catalog).append("*/");
        key.append(query);
        return key.toString();
    }

    @Benchmark
    @BenchmarkMode(Mode.Throughput)
    public void testCompoundCacheKeyNewHashCode() throws Exception {
        new CompoundCacheKey("test", "select this_.id as id1_13_0_, this_.cost as cost2_13_0_, this_.local_currency as local_cu3_13_0_, this_.player_id as player_i4_13_0_, this_.receipt_data as receipt_5_13_0_, this_.retry_attempts as retry_at6_13_0_, this_.transaction_id as transact7_13_0_ from appstore_retry_queue this_");
    }

    @Benchmark
    @BenchmarkMode(Mode.Throughput)
    public void testCompoundCacheKeyOldHashCode() throws Exception {
        new CompoundCacheKeyOldHashCode("test", "select this_.id as id1_13_0_, this_.cost as cost2_13_0_, this_.local_currency as local_cu3_13_0_, this_.player_id as player_i4_13_0_, this_.receipt_data as receipt_5_13_0_, this_.retry_attempts as retry_at6_13_0_, this_.transaction_id as transact7_13_0_ from appstore_retry_queue this_");
    }

    @Benchmark
    @BenchmarkMode(Mode.Throughput)
    public void testSimpleKey() throws Exception {
        new SimpleKey("test", "select this_.id as id1_13_0_, this_.cost as cost2_13_0_, this_.local_currency as local_cu3_13_0_, this_.player_id as player_i4_13_0_, this_.receipt_data as receipt_5_13_0_, this_.retry_attempts as retry_at6_13_0_, this_.transaction_id as transact7_13_0_ from appstore_retry_queue this_");
    }

    @Benchmark
    @BenchmarkMode(Mode.Throughput)
    public void testStringBuilder() throws Exception {
        makePreparedStatementCacheKey("test", "select this_.id as id1_13_0_, this_.cost as cost2_13_0_, this_.local_currency as local_cu3_13_0_, this_.player_id as player_i4_13_0_, this_.receipt_data as receipt_5_13_0_, this_.retry_attempts as retry_at6_13_0_, this_.transaction_id as transact7_13_0_ from appstore_retry_queue this_");
    }

    static class CompoundCacheKeyOldHashCode {
        String componentOne;

        String componentTwo;

        int hashCode;

        CompoundCacheKeyOldHashCode(String partOne, String partTwo) {
            this.componentOne = partOne;
            this.componentTwo = partTwo;
            // Handle first component (in most cases, currentCatalog being NULL....
            this.hashCode = (((this.componentOne != null) ? this.componentOne : "") + this.componentTwo).hashCode();
        }

        /*
         * (non-Javadoc)
         *
         * @see java.lang.Object#equals(java.lang.Object)
         */
        @Override
        public boolean equals(Object obj) {
            if (obj instanceof CompoundCacheKeyOldHashCode) {
                CompoundCacheKeyOldHashCode another = (CompoundCacheKeyOldHashCode) obj;

                boolean firstPartEqual = false;

                if (this.componentOne == null) {
                    firstPartEqual = (another.componentOne == null);
                } else {
                    firstPartEqual = this.componentOne.equals(another.componentOne);
                }

                return (firstPartEqual && this.componentTwo.equals(another.componentTwo));
            }

            return false;
        }

        /*
         * (non-Javadoc)
         *
         * @see java.lang.Object#hashCode()
         */
        @Override
        public int hashCode() {
            return this.hashCode;
        }
    }

    static class CompoundCacheKey {
        final String componentOne;

        final String componentTwo;

        final int hashCode;

        CompoundCacheKey(String partOne, String partTwo) {
            this.componentOne = partOne;
            this.componentTwo = partTwo;
            // Handle first component (in most cases, currentCatalog being NULL....
            this.hashCode = 31 * (componentOne != null ? componentOne.hashCode() : 0) + (componentTwo != null ? componentTwo.hashCode() : 0);
        }

        /*
         * (non-Javadoc)
         *
         * @see java.lang.Object#equals(java.lang.Object)
         */
        @Override
        public boolean equals(Object obj) {
            if (obj instanceof CompoundCacheKey) {
                CompoundCacheKey another = (CompoundCacheKey) obj;

                boolean firstPartEqual = false;

                if (this.componentOne == null) {
                    firstPartEqual = (another.componentOne == null);
                } else {
                    firstPartEqual = this.componentOne.equals(another.componentOne);
                }

                return (firstPartEqual && this.componentTwo.equals(another.componentTwo));
            }

            return false;
        }

        /*
         * (non-Javadoc)
         *
         * @see java.lang.Object#hashCode()
         */
        @Override
        public int hashCode() {
            return this.hashCode;
        }
    }

    private final class SimpleKey {
        private final String catalog;
        private final String query;

        public SimpleKey(String catalog, String query) {
            this.catalog = catalog;
            this.query = query;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            SimpleKey simpleKey = (SimpleKey) o;

            if (catalog != null ? !catalog.equals(simpleKey.catalog) : simpleKey.catalog != null) return false;
            return query != null ? query.equals(simpleKey.query) : simpleKey.query == null;
        }

        @Override
        public int hashCode() {
            int result = catalog != null ? catalog.hashCode() : 0;
            result = 31 * result + (query != null ? query.hashCode() : 0);
            return result;
        }
    }
}

Benchmark                                        Mode  Cnt           Score          Error  Units
AllocationTest.testCompoundCacheKeyNewHashCode  thrpt  100  1471082435.003 ± 30337517.290  ops/s
AllocationTest.testCompoundCacheKeyOldHashCode  thrpt  100     2950018.596 ±     8728.735  ops/s
AllocationTest.testSimpleKey                    thrpt  100  3778832816.385 ± 18671795.473  ops/s
AllocationTest.testStringBuilder                thrpt  100     5881551.927 ±    47208.040  ops/s

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[mysql-oca-bot]

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[johnou]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow
bug http://bugs.mysql.com/bug.php?id=88021 for updates.
Thanks