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Zero garbage serialization of ISO timestamps (#77)
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132 changes: 132 additions & 0 deletions
132
apm-agent-core/src/main/java/co/elastic/apm/report/serialize/DateSerializer.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,132 @@ | ||
| /*- | ||
| * #%L | ||
| * Elastic APM Java agent | ||
| * %% | ||
| * Copyright (C) 2018 the original author or authors | ||
| * %% | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| * #L% | ||
| */ | ||
| package co.elastic.apm.report.serialize; | ||
|
|
||
| import com.dslplatform.json.JsonWriter; | ||
| import com.dslplatform.json.NumberConverter; | ||
|
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| import java.text.SimpleDateFormat; | ||
| import java.util.Date; | ||
| import java.util.TimeZone; | ||
|
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| /** | ||
| * This class serializes an epoch timestamp in milliseconds to a ISO 8601 date time sting, | ||
| * for example {@code 1970-01-01T00:00:00.000Z} | ||
| * <p> | ||
| * The main advantage of this class is that is able to serialize the timestamp in a garbage free way, | ||
| * i.e. without object allocations and that it is faster than {@link java.text.DateFormat#format(Date)}. | ||
| * </p> | ||
| * <p> | ||
| * The most complex part when formatting a ISO date is to determine the actual year, | ||
| * month and date as you have to account for leap years. | ||
| * Leveraging the fact that for a whole day this stays the same | ||
| * and that the agent only serializes the current timestamp and not arbitrary ones, | ||
| * we offload this task to {@link java.text.DateFormat#format(Date)} and cache the result. | ||
| * So we only have to serialize the time part of the ISO timestamp which is easy | ||
| * as a day has exactly {@code 1000 * 60 * 60 * 24} milliseconds. | ||
| * Also, we don't have to worry about leap seconds when dealing with the epoch timestamp. | ||
| * </p> | ||
| * <p> | ||
| * Note: this class is not thread safe. | ||
| * As serializing the payloads is done in a single thread, | ||
| * this is no problem though. | ||
| * </p> | ||
| */ | ||
| class DateSerializer { | ||
|
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| private static final long MILLIS_PER_SECOND = 1000; | ||
| private static final long MILLIS_PER_MINUTE = MILLIS_PER_SECOND * 60; | ||
| private static final long MILLIS_PER_HOUR = MILLIS_PER_MINUTE * 60; | ||
| private static final long MILLIS_PER_DAY = MILLIS_PER_HOUR * 24; | ||
| private static final byte TIME_SEPARATOR = 'T'; | ||
| private static final byte TIME_ZONE_SEPARATOR = 'Z'; | ||
| private static final byte COLON = ':'; | ||
| private static final byte DOT = '.'; | ||
| private static final byte ZERO = '0'; | ||
| private final SimpleDateFormat dateFormat; | ||
| // initialized in constructor via cacheDate | ||
| @SuppressWarnings("NullableProblems") | ||
| private String cachedDateIso; | ||
| private long startOfCachedDate; | ||
| private long endOfCachedDate; | ||
|
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| DateSerializer() { | ||
| dateFormat = new SimpleDateFormat("yyyy-MM-dd"); | ||
| dateFormat.setTimeZone(TimeZone.getTimeZone("UTC")); | ||
| cacheDate(System.currentTimeMillis()); | ||
| } | ||
|
|
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| private static long atStartOfDay(long epochTimestamp) { | ||
| return epochTimestamp - epochTimestamp % MILLIS_PER_DAY; | ||
| } | ||
|
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| private static long atEndOfDay(long epochTimestamp) { | ||
| return atStartOfDay(epochTimestamp) + MILLIS_PER_DAY - 1; | ||
| } | ||
|
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| void serializeEpochTimestampAsIsoDateTime(JsonWriter jw, long epochTimestamp) { | ||
| if (!isDateCached(epochTimestamp)) { | ||
| cacheDate(epochTimestamp); | ||
| } | ||
| jw.writeAscii(cachedDateIso); | ||
|
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| jw.writeByte(TIME_SEPARATOR); | ||
|
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| // hours | ||
| long remainder = epochTimestamp % MILLIS_PER_DAY; | ||
| serializeWithLeadingZero(jw, remainder / MILLIS_PER_HOUR, 2); | ||
| jw.writeByte(COLON); | ||
|
|
||
| // minutes | ||
| remainder %= MILLIS_PER_HOUR; | ||
| serializeWithLeadingZero(jw, remainder / MILLIS_PER_MINUTE, 2); | ||
| jw.writeByte(COLON); | ||
|
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| // seconds | ||
| remainder %= MILLIS_PER_MINUTE; | ||
| serializeWithLeadingZero(jw, remainder / MILLIS_PER_SECOND, 2); | ||
| jw.writeByte(DOT); | ||
|
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| // milliseconds | ||
| remainder %= MILLIS_PER_SECOND; | ||
| serializeWithLeadingZero(jw, remainder, 3); | ||
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| jw.writeByte(TIME_ZONE_SEPARATOR); | ||
| } | ||
|
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| private void serializeWithLeadingZero(JsonWriter jw, long value, int minLength) { | ||
| for (int i = minLength - 1; i > 0; i--) { | ||
| if (value < Math.pow(10, i)) { | ||
| jw.writeByte(ZERO); | ||
| } | ||
| } | ||
| NumberConverter.serialize(value, jw); | ||
| } | ||
|
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| private void cacheDate(long epochTimestamp) { | ||
| cachedDateIso = dateFormat.format(new Date(epochTimestamp)); | ||
| startOfCachedDate = atStartOfDay(epochTimestamp); | ||
| endOfCachedDate = atEndOfDay(epochTimestamp); | ||
| } | ||
|
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| private boolean isDateCached(long epochTimestamp) { | ||
| return epochTimestamp >= startOfCachedDate && epochTimestamp <= endOfCachedDate; | ||
| } | ||
| } |
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69
apm-agent-core/src/test/java/co/elastic/apm/report/serialize/DateSerializerTest.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| /*- | ||
| * #%L | ||
| * Elastic APM Java agent | ||
| * %% | ||
| * Copyright (C) 2018 the original author or authors | ||
| * %% | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| * #L% | ||
| */ | ||
| package co.elastic.apm.report.serialize; | ||
|
|
||
| import com.dslplatform.json.DslJson; | ||
| import com.dslplatform.json.JsonWriter; | ||
| import org.junit.jupiter.api.BeforeEach; | ||
| import org.junit.jupiter.api.Test; | ||
|
|
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| import java.time.Instant; | ||
| import java.time.LocalDateTime; | ||
| import java.time.ZoneId; | ||
| import java.time.ZoneOffset; | ||
| import java.time.format.DateTimeFormatter; | ||
| import java.time.temporal.ChronoUnit; | ||
|
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| import static org.assertj.core.api.Assertions.assertThat; | ||
|
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| class DateSerializerTest { | ||
|
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| private DateSerializer dateSerializer; | ||
| private JsonWriter jsonWriter; | ||
| private DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'").withZone(ZoneId.of("UTC")); | ||
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| @BeforeEach | ||
| void setUp() { | ||
| jsonWriter = new DslJson<>().newWriter(); | ||
| dateSerializer = new DateSerializer(); | ||
| } | ||
|
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| @Test | ||
| void testSerializeEpochTimestampAsIsoDateTime() { | ||
| long timestamp = 0; | ||
| long lastTimestampToCheck = LocalDateTime.now() | ||
| .plus(1, ChronoUnit.YEARS) | ||
| .toInstant(ZoneOffset.UTC) | ||
| .toEpochMilli(); | ||
| // interval is approximately a hour but not exactly | ||
| // to get different values for the minutes, seconds and milliseconds | ||
| long interval = 997 * 61 * 61; | ||
| for (; timestamp <= lastTimestampToCheck; timestamp += interval) { | ||
| assertDateFormattingIsCorrect(Instant.ofEpochMilli(timestamp)); | ||
| } | ||
| } | ||
|
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| private void assertDateFormattingIsCorrect(Instant instant) { | ||
| jsonWriter.reset(); | ||
| dateSerializer.serializeEpochTimestampAsIsoDateTime(jsonWriter, instant.toEpochMilli()); | ||
| assertThat(jsonWriter.toString()).isEqualTo(dateTimeFormatter.format(instant)); | ||
| } | ||
| } |