diff --git a/fe/fe-core/src/main/java/org/apache/doris/planner/ScanNode.java b/fe/fe-core/src/main/java/org/apache/doris/planner/ScanNode.java index a0b5d5911cfae2..3e25bd6e7f8d4a 100644 --- a/fe/fe-core/src/main/java/org/apache/doris/planner/ScanNode.java +++ b/fe/fe-core/src/main/java/org/apache/doris/planner/ScanNode.java @@ -746,8 +746,9 @@ public int getScanRangeNum() { return Integer.MAX_VALUE; } - public boolean shouldUseOneInstance() { - return hasLimit() && conjuncts.isEmpty(); + public boolean shouldUseOneInstance(ConnectContext ctx) { + long limitRowsForSingleInstance = ctx == null ? 10000 : ctx.getSessionVariable().limitRowsForSingleInstance; + return hasLimit() && getLimit() < limitRowsForSingleInstance && conjuncts.isEmpty(); } // In cloud mode, meta read lock is not enough to keep a snapshot of the partition versions. diff --git a/fe/fe-core/src/main/java/org/apache/doris/qe/Coordinator.java b/fe/fe-core/src/main/java/org/apache/doris/qe/Coordinator.java index 73979aefc3ed4d..83f072a6bf1f20 100644 --- a/fe/fe-core/src/main/java/org/apache/doris/qe/Coordinator.java +++ b/fe/fe-core/src/main/java/org/apache/doris/qe/Coordinator.java @@ -2082,7 +2082,7 @@ private void computeFragmentHosts() throws Exception { expectedInstanceNum = Math.max(expectedInstanceNum, 1); // if have limit and no conjuncts, only need 1 instance to save cpu and // mem resource - if (node.get().shouldUseOneInstance()) { + if (node.get().shouldUseOneInstance(context)) { expectedInstanceNum = 1; } @@ -2095,7 +2095,7 @@ private void computeFragmentHosts() throws Exception { } // if have limit and no conjuncts, only need 1 instance to save cpu and // mem resource - if (node.get().shouldUseOneInstance()) { + if (node.get().shouldUseOneInstance(context)) { expectedInstanceNum = 1; } diff --git a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java index 930fd0ad84a93e..5b0512683aa486 100644 --- a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java +++ b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java @@ -554,6 +554,8 @@ public class SessionVariable implements Serializable, Writable { public static final String ENABLE_STATS = "enable_stats"; + public static final String LIMIT_ROWS_FOR_SINGLE_INSTANCE = "limit_rows_for_single_instance"; + // CLOUD_VARIABLES_BEGIN public static final String CLOUD_CLUSTER = "cloud_cluster"; public static final String DISABLE_EMPTY_PARTITION_PRUNE = "disable_empty_partition_prune"; @@ -1081,7 +1083,6 @@ public void setMaxJoinNumberOfReorder(int maxJoinNumberOfReorder) { this.maxJoinNumberOfReorder = maxJoinNumberOfReorder; } - @VariableMgr.VarAttr(name = MAX_JOIN_NUMBER_BUSHY_TREE) private int maxJoinNumBushyTree = 8; @@ -1124,6 +1125,14 @@ public void setMaxJoinNumberOfReorder(int maxJoinNumberOfReorder) { @VariableMgr.VarAttr(name = NTH_OPTIMIZED_PLAN) private int nthOptimizedPlan = 1; + @VariableMgr.VarAttr(name = LIMIT_ROWS_FOR_SINGLE_INSTANCE, + description = {"当一个 ScanNode 上没有过滤条件,且 limit 值小于这个阈值时," + + "系统会将这个算子的并发度调整为1,以减少简单查询的扇出", + "When a ScanNode has no filter conditions and the limit value is less than this threshold, " + + "the system will adjust the concurrency of this operator to 1 " + + "to reduce the fan-out of simple queries"}) + public long limitRowsForSingleInstance = 10000; + public boolean isEnableLeftZigZag() { return enableLeftZigZag; }