背景
本文来从底层代码的实现来分析一下Starrocks怎么获取统计信息，这些统计信息在后续基于CBO的代价计算的时候有着重要的作用
本文基于Starrrocks 3.3.5
结论
Starrocks的统计信息的收集是通过周期性的运行一系列的SQL（以分区为维度，如果不是分区表，其实也有个默认的分区,也就是单个分区），之后插入到_statistics_.column_statistics表中,并会存储在 GlobalStateMgr.CachedStatisticStorage，后续所有的统计信息的获取也是通过这里获取的
分析
直接到StatisticAutoCollector类
public StatisticAutoCollector() {
super("AutoStatistic", Config.statistic_collect_interval_sec * 1000);
}这里默认的调度周期是 statistic_collect_interval_sec (也就是5分钟)
@Override
protected void runAfterCatalogReady() {
// update interval
if (getInterval() != Config.statistic_collect_interval_sec * 1000) {
setInterval(Config.statistic_collect_interval_sec * 1000);
}
if (!Config.enable_statistic_collect || FeConstants.runningUnitTest) {
return;
}
if (!checkoutAnalyzeTime(LocalTime.now(TimeUtils.getTimeZone().toZoneId()))) {
return;
}
// check statistic table state
if (!StatisticUtils.checkStatisticTableStateNormal()) {
return;
}
initDefaultJob();
runJobs();
}-
强制 调度周期设置为5分钟
-
进行 调度时间的检查，默认是一天，也可以设置开始和结束时间,
statistic_auto_analyze_start_time,statistic_auto_analyze_end_time -
还可以设置enable_statistic_collect为false，如果不想进行统计信息的采集的话
-
initDefaultJob 初始化统计信息采集任务,默认是
enable_collect_full_statistic为 true,也就是全量采集 -
runJobs 运行采集任务，也就是最核心的阶段
protected List<StatisticsCollectJob> runJobs() { ... Set<Long> analyzeTableSet = Sets.newHashSet(); for (NativeAnalyzeJob nativeAnalyzeJob : allNativeAnalyzeJobs) { List<StatisticsCollectJob> jobs = nativeAnalyzeJob.instantiateJobs(); result.addAll(jobs); ConnectContext statsConnectCtx = StatisticUtils.buildConnectContext(); statsConnectCtx.setThreadLocalInfo(); nativeAnalyzeJob.run(statsConnectCtx, STATISTIC_EXECUTOR, jobs); for (StatisticsCollectJob job : jobs) { if (job.isAnalyzeTable()) { analyzeTableSet.add(job.getTable().getId()); } } } LOG.info("auto collect statistic on analyze job[{}] end", analyzeJobIds); if (Config.enable_collect_full_statistic) { LOG.info("auto collect full statistic on all databases start"); List<StatisticsCollectJob> allJobs = StatisticsCollectJobFactory.buildStatisticsCollectJob(createDefaultJobAnalyzeAll()); for (StatisticsCollectJob statsJob : allJobs) { // user-created analyze job has a higher priority if (statsJob.isAnalyzeTable() && analyzeTableSet.contains(statsJob.getTable().getId())) { continue; } result.add(statsJob); AnalyzeStatus analyzeStatus = new NativeAnalyzeStatus(GlobalStateMgr.getCurrentState().getNextId(), statsJob.getDb().getId(), statsJob.getTable().getId(), statsJob.getColumnNames(), statsJob.getType(), statsJob.getScheduleType(), statsJob.getProperties(), LocalDateTime.now()); analyzeStatus.setStatus(StatsConstants.ScheduleStatus.FAILED); GlobalStateMgr.getCurrentState().getAnalyzeMgr().addAnalyzeStatus(analyzeStatus); ConnectContext statsConnectCtx = StatisticUtils.buildConnectContext(); statsConnectCtx.setThreadLocalInfo(); STATISTIC_EXECUTOR.collectStatistics(statsConnectCtx, statsJob, analyzeStatus, true); } LOG.info("auto collect full statistic on all databases end"); } ... return result; }-
nativeAnalyzeJob.instantiateJobs 构造统计信息
这里调用了StatisticsCollectJobFactory.buildStatisticsCollectJob方法,
首先这里有个配置statistic_exclude_pattern可以排除不需要进行统计的表（以db.table格式）
其次是会根据当前所谓的健康度（也就是分区更新的时间比例）和statistic_auto_collect_ratio大小比较，如果健康度小于该值，则调用createFullStatsJob方法，创建全量统计任务。
这里 主要用buildStatisticsCollectJob构造一个FullStatisticsCollectJob类型的job -
nativeAnalyzeJob.run 运行统计信息任务
这个方法会调用StatisticExecutor.collectStatistics，最终会调用FullStatisticsCollectJob.collect方法int parallelism = Math.max(1, context.getSessionVariable().getStatisticCollectParallelism()); List<List<String>> collectSQLList = buildCollectSQLList(parallelism); long totalCollectSQL = collectSQLList.size(); ... Exception lastFailure = null; for (List<String> sqlUnion : collectSQLList) { if (sqlUnion.size() < parallelism) { context.getSessionVariable().setPipelineDop(parallelism / sqlUnion.size()); } else { context.getSessionVariable().setPipelineDop(1); } String sql = Joiner.on(" UNION ALL ").join(sqlUnion); try { collectStatisticSync(sql, context); } catch (Exception e) { ... } finishedSQLNum++; analyzeStatus.setProgress(finishedSQLNum * 100 / totalCollectSQL); GlobalStateMgr.getCurrentState().getAnalyzeMgr().addAnalyzeStatus(analyzeStatus); } ... flushInsertStatisticsData(context, true);-
首先设置一个 运行sql的并行度
statistic_collect_parallel默认是1，这个意思就是这个统计sql会分多少次运行 -
buildCollectSQLList 这里会构建具体运行统计信息的SQL，这会具体的分区级别
-
collectStatisticSync 这里会执行具体的SQL
SQL如下：SELECT cast(4 as INT) , cast($partitionId as BIGINT) , '$columnNameStr' , cast(COUNT(1) as BIGINT) , cast($dataSize as BIGINT) , hex(hll_serialize(IFNULL(hll_raw(column_key), hll_empty()))), cast( (COUNT(1) - COUNT(column_key)) as BIGINT) , MAX(column_key) , MIN(column_key) FROM (select $quoteColumnName as column_key from `$dbName`.`$tableName` partition `$partitionName`) tt -
flushInsertStatisticsData 这里会把执行的结果数据存储到
_statistics_.column_statistics
-
-
analyzeMgr.refreshBasicStatisticsCache这个主要的作用是 更新CachedStatisticStorage 里的统计信息
主要通过 refreshTableStatistic 和 getColumnStatistics
这两个方法分别会调用 TableStatsCacheLoader 和 ColumnBasicStatsCacheLoader 去执行SQL从而获取对应的统计信息，调用的SQL如下：select cast(3 as INT), partition_id, any_value(row_count) FROM column_statistics WHERE table_id = $tableId and partition_id = $partitionId GROUP BY partition_id; SELECT cast( 1 as INT), $updateTime, db_id, table_id, column_name, sum(row_count), cast(sum(data_size) as bigint), hll_union_agg(ndv), sum(null_count), cast(max(cast(max as $type)) as string), cast(min(cast(min as $type)) as string) FROM column_statistics WHERE table_id = $table_id and column_name in (xxx,xxx,xxx) GROUP BY db_id, table_id, column_name;
-
其他
-
StatisticAutoCollector 是通过周期性的任务来进行统计信息的收集
-
手动的收集
ANALYZE TABLE
如命令：ANALYZE [FULL|SAMPLE] TABLE tbl_name (col_name [,col_name]) [WITH SYNC | ASYNC MODE] PROPERTIES (property [,property]) -
手动触发自动收集
CREATE ANALYZE
如命令：CREATE ANALYZE [FULL|SAMPLE] TABLE tbl_name (col_name [,col_name]) PROPERTIES (property [,property])
以上都会触发统计信息的收集。