pettyjamesm

Initial observations about FlatGroupByHash memory usage compared to the previous MultiChannelGroupByHash that was removed in Trino 427 are documented in this gist. Those observations prompted a deeper investigation and discussion how FlatHash and the flat layout scheme should work and was carried forward into a reimplementation in trino#25127.

Summary of Changes

1. Reduce the flat memory layout width for variable width types from 16 to 4 bytes per entry
2. Reduce the expansion factor of VariableWidthData from 2x to 1.5x

pettyjamesm

[
    {
        "jmhVersion" : "1.37",
        "benchmark" : "io.trino.operator.BenchmarkGroupByHash.addPages",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/Users/user/.sdkman/candidates/java/23.0.1-tem/bin/java",
        "jvmArgs" : [
            "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=52578:/Applications/IntelliJ IDEA.app/Contents/bin",

pettyjamesm

[
    {
        "jmhVersion" : "1.37",
        "benchmark" : "io.trino.operator.BenchmarkTopNOperator.topN",
        "mode" : "thrpt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/Users/pettja/.sdkman/candidates/java/23.0.1-tem/bin/java",
        "jvmArgs" : [
            "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=54654:/Applications/IntelliJ IDEA.app/Contents/bin",

pettyjamesm

[
    {
        "jmhVersion" : "1.37",
        "benchmark" : "io.trino.operator.BenchmarkGroupByHash.addPages",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/17.0.8-amzn/bin/java",
        "jvmArgs" : [
            "-Xms10g",

pettyjamesm

[
    {
        "jmhVersion" : "1.37",
        "benchmark" : "io.trino.operator.BenchmarkGroupByHash.addPages",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/17.0.8-amzn/bin/java",
        "jvmArgs" : [
            "-Xms10g",

pettyjamesm

[
    {
        "jmhVersion" : "1.36",
        "benchmark" : "io.trino.operator.BenchmarkGroupedTopNRowNumberBuilder.processTopNInput",
        "mode" : "thrpt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/17.0.6-amzn/bin/java",
        "jvmArgs" : [
            "-Xms4g",

pettyjamesm

[
    {
        "jmhVersion" : "1.35",
        "benchmark" : "io.trino.operator.scalar.timestamp.BenchmarkCastTimestampToVarchar.benchmarkCastToVarchar",
        "mode" : "thrpt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/Users/pettja/.sdkman/candidates/java/17.0.5-amzn/bin/java",
        "jvmArgs" : [
            "-Djdk.attach.allowAttachSelf",

pettyjamesm

[
    {
        "jmhVersion" : "1.20",
        "benchmark" : "com.facebook.presto.block.BenchmarkBlocks.benchmarkGetPositionsSizeInBytes",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/8.312.07.1-amzn/jre/bin/java",
        "jvmArgs" : [

pettyjamesm

[
    {
        "jmhVersion" : "1.20",
        "benchmark" : "com.facebook.presto.block.BenchmarkBlocks.benchmarkCopyPositions",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/8.0.265-amzn/jre/bin/java",
        "jvmArgs" : [
            "-Xms8g",

pettyjamesm

[
    {
        "jmhVersion" : "1.20",
        "benchmark" : "io.trino.benchmark.BenchmarkInequalityJoin.benchmarkJoin",
        "mode" : "avgt",
        "threads" : 1,
        "forks" : 1,
        "jvm" : "/local/home/pettja/.sdkman/candidates/java/11.0.12-zulu/bin/java",
        "jvmArgs" : [
            "-Xms8g",