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• SQL如何一步步变成执行计划的
• 有哪些优化器，哪些优化规则
• calcite 和flink 如何结合的

测试代码

EnvironmentSettings settings = EnvironmentSettings.inBatchMode();
TableEnvironment tableEnvironment = TableEnvironment.create(settings);Schema schema = Schema.newBuilder().column("count", DataTypes.INT()).column("word", DataTypes.STRING()).build();Schema schema1 = Schema.newBuilder().column("id", DataTypes.INT()).column("name", DataTypes.STRING()).build();tableEnvironment.createTemporaryTable("aa_user", TableDescriptor.forConnector("filesystem").schema(schema).option("path", "/Users/xx/IdeaProjects/flink-demo/data/order.csv").format("csv").build());tableEnvironment.createTemporaryTable("bb_order", TableDescriptor.forConnector("filesystem").schema(schema1).option("path", "/Users/xx/IdeaProjects/flink-demo/data/user.csv").format("csv").build());String cost = tableEnvironment.explainSql("select * from aa_user inner join bb_order on `aa_user`.`count`=`bb_order`.`id`", ExplainDetail.ESTIMATED_COST);System.out.println(cost);

背景知识

需要了解calcite 里的基本知识，如AST,RelNode ,hepPlanner等等。
需要了解Flink 和Flink SQL里的一些知识

SQL转变流程图

SQL经过flink 里注册的每一个优化器，优化后，就能变成物理计划了，不过要变成执行代码，还要再经过代码生成。

问题

• 问题1，FlinkBatchProgram
  所有flink优化器都是在这个类里添加的

object FlinkBatchProgram {val SUBQUERY_REWRITE = "subquery_rewrite"val TEMPORAL_JOIN_REWRITE = "temporal_join_rewrite"val DECORRELATE = "decorrelate"val DEFAULT_REWRITE = "default_rewrite"val PREDICATE_PUSHDOWN = "predicate_pushdown"val JOIN_REORDER = "join_reorder"val JOIN_REWRITE = "join_rewrite"val PROJECT_REWRITE = "project_rewrite"val WINDOW = "window"val LOGICAL = "logical"val LOGICAL_REWRITE = "logical_rewrite"val TIME_INDICATOR = "time_indicator"val PHYSICAL = "physical"val PHYSICAL_REWRITE = "physical_rewrite"val DYNAMIC_PARTITION_PRUNING = "dynamic_partition_pruning"val RUNTIME_FILTER = "runtime_filter}

• 问题2，calcite 优化器和flink 如何结合的
  logical，physical 这两个优化器都是用的VolcanoPlanner，结合规则和代价。
  剩下的优化器HepPlanner，HepPlanner 完全使用规则。

• 问题3，project_rewrite 后，为啥少了LogicalProject ReNode ?
  因为最后一个操作，logicalproject 这里就是把所有的字段查出来了，所有这一步实际上是不用的

• 问题4，物理计划如何生成执行代码的？
  BatchPhysicalTableSourceScan 类

class BatchPhysicalTableSourceScan(cluster: RelOptCluster,traitSet: RelTraitSet,hints: util.List[RelHint],tableSourceTable: TableSourceTable)extends CommonPhysicalTableSourceScan(cluster, traitSet, hints, tableSourceTable)with BatchPhysicalRel {override def computeSelfCost(planner: RelOptPlanner, mq: RelMetadataQuery): RelOptCost = {val rowCnt = mq.getRowCount(this)if (rowCnt == null) {return null}val cpu = 0val rowSize = mq.getAverageRowSize(this)val size = rowCnt * rowSizeplanner.getCostFactory.makeCost(rowCnt, cpu, size)}// 这里生成的执行代码override def translateToExecNode(): ExecNode[_] = {val tableSourceSpec = new DynamicTableSourceSpec(tableSourceTable.contextResolvedTable,util.Arrays.asList(tableSourceTable.abilitySpecs: _*))tableSourceSpec.setTableSource(tableSourceTable.tableSource)new BatchExecTableSourceScan(unwrapTableConfig(this),tableSourceSpec,FlinkTypeFactory.toLogicalRowType(getRowType),getRelDetailedDescription)}
}

• 问题5，为啥aa_user 表被广播，哪里实现的？

BatchPhysicalHashJoinRule 规则实现的

核心代码

 val leftSize = JoinUtil.binaryRowRelNodeSize(join.getLeft)val rightSize = JoinUtil.binaryRowRelNodeSize(join.getRight)// if it is not with hint, just check size of left and right side by statistic and config// if leftSize or rightSize is unknown, cannot use broadcastif (leftSize == null || rightSize == null) {return (false, false)}val threshold =tableConfig.get(OptimizerConfigOptions.TABLE_OPTIMIZER_BROADCAST_JOIN_THRESHOLD)val rightSizeSmallerThanThreshold = rightSize <= thresholdval leftSizeSmallerThanThreshold = leftSize <= thresholdval leftSmallerThanRight = leftSize < rightSizejoin.getJoinType match {case JoinRelType.LEFT => (rightSizeSmallerThanThreshold, false)case JoinRelType.RIGHT => (leftSizeSmallerThanThreshold, true)case JoinRelType.FULL => (false, false)case JoinRelType.INNER =>(leftSizeSmallerThanThreshold|| rightSizeSmallerThanThreshold,leftSmallerThanRight)// left side cannot be used as build side in SEMI/ANTI join.case JoinRelType.SEMI | JoinRelType.ANTI =>(rightSizeSmallerThanThreshold, false)}

主要就是实现

  def binaryRowRelNodeSize(relNode: RelNode): JDouble = {val mq = relNode.getCluster.getMetadataQueryval rowCount = mq.getRowCount(relNode)if (rowCount == null) {null} else {rowCount * FlinkRelMdUtil.binaryRowAverageSize(relNode)}}

最后还是到了FlinkRelMdColumnNullCount 这个类
从这个ts: TableScan 对象里取出来
那ts 对象又是在哪里赋值的，看这个FlinkRecomputeStatisticsProgram 类

class FlinkRelMdColumnNullCount private extends MetadataHandler[ColumnNullCount] {override def getDef: MetadataDef[ColumnNullCount] = FlinkMetadata.ColumnNullCount.DEF/*** Gets the null count of the given column in TableScan.** @param ts*   TableScan RelNode* @param mq*   RelMetadataQuery instance* @param index*   the index of the given column* @return*   the null count of the given column in TableScan*/def getColumnNullCount(ts: TableScan, mq: RelMetadataQuery, index: Int): JDouble = {Preconditions.checkArgument(mq.isInstanceOf[FlinkRelMetadataQuery])val relOptTable = ts.getTable.asInstanceOf[FlinkPreparingTableBase]val fieldNames = relOptTable.getRowType.getFieldNamesPreconditions.checkArgument(index >= 0 && index < fieldNames.size())val fieldName = fieldNames.get(index)val statistic = relOptTable.getStatisticval colStats = statistic.getColumnStats(fieldName)if (colStats != null && colStats.getNullCount != null) {colStats.getNullCount.toDouble} else {null}}}

ts是在这里赋值，这里最后会用调用具体的文件系统，找到文件行数

 private LogicalTableScan recomputeStatistics(LogicalTableScan scan) {final RelOptTable scanTable = scan.getTable();if (!(scanTable instanceof TableSourceTable)) {return scan;}FlinkContext context = ShortcutUtils.unwrapContext(scan);TableSourceTable table = (TableSourceTable) scanTable;boolean reportStatEnabled =context.getTableConfig().get(TABLE_OPTIMIZER_SOURCE_REPORT_STATISTICS_ENABLED)&& table.tableSource() instanceof SupportsStatisticReport;SourceAbilitySpec[] specs = table.abilitySpecs();PartitionPushDownSpec partitionPushDownSpec = getSpec(specs, PartitionPushDownSpec.class);FilterPushDownSpec filterPushDownSpec = getSpec(specs, FilterPushDownSpec.class);TableStats newTableStat =recomputeStatistics(table, partitionPushDownSpec, filterPushDownSpec, reportStatEnabled);FlinkStatistic newStatistic =FlinkStatistic.builder().statistic(table.getStatistic()).tableStats(newTableStat).build();TableSourceTable newTable = table.copy(newStatistic);return new LogicalTableScan(scan.getCluster(), scan.getTraitSet(), scan.getHints(), newTable);}