网站设计怎么做图片透明度,dw8做网站步骤图,天健emp软件开发平台,个人信息网站模板相关 《Postgresql源码#xff08;131#xff09;行锁的原理分析》 1 分布式行锁
PG中的行锁在上一片中做了分析《Postgresql源码#xff08;131#xff09;行锁的原理分析》#xff0c;本篇对分布式PG#xff08;PGXL#xff09;中的行锁做一些分析。#xff08;版本… 相关 《Postgresql源码131行锁的原理分析》 1 分布式行锁
PG中的行锁在上一片中做了分析《Postgresql源码131行锁的原理分析》本篇对分布式PGPGXL中的行锁做一些分析。版本Postgres-XL 10alpha2
2 计划生成pgxc_planner
分布式PG中的计划生成有两个入口
pgxc_plannerresult pgxc_FQS_planner(query, cursorOptions, boundParams);if (result) return result;result standard_planner(query, cursorOptions, boundParams);return result;pgxc_FQS_plannerFast Query Shipping planner尝试确定一个查询是否可以完全在DN上执行不需要CN节点参与计算。FQS计划比较简单直接把SQL发到某几个DN上跑。standard_planner是标准查询规划器。
查询首先通过pgxc_FQS_planner看是否适合快速分发。如果不适合会继续走standard_planner。
2.1 pgxc_FQS_planner生成FQS计划
XL默认对行锁的SQL不能走FQS这里为了简单介绍下FQS用了一个点查的例子。
用例
drop table TBL_33;
create table TBL_33(c3 int);
insert into TBL_33 values(0);
SELECT c3 FROM TBL_33 WHERE c30;;分布式执行计划
explain SELECT c3 FROM TBL_33 WHERE c30;QUERY PLAN
---------------------------------------------------------------Remote Fast Query Execution (cost0.00..0.00 rows0 width0)Node/s: datanode_2- Seq Scan on tbl_33 (cost0.00..41.88 rows13 width4)Filter: (c3 0)pgxc_FQS_planner
static PlannedStmt *
pgxc_FQS_planner(Query *query, int cursorOptions, ParamListInfo boundParams)
{用规则过滤一些不能FQS的情况 if (!enable_fast_query_shipping)return NULL;if (cursorOptions CURSOR_OPT_SCROLL)return NULL;if (query-utilityStmt IsA(query-utilityStmt, RemoteQuery)){RemoteQuery *stmt (RemoteQuery *) query-utilityStmt;if (stmt-exec_direct_type ! EXEC_DIRECT_NONE)return NULL;}
遍历查询树用一些规则排除不能FQS的情况。pgxc_shippability_walker函数在遍历的同时会维护一个bitmapsc_context.sc_shippability里面记录了不能ship的各种原因最后在pgxc_is_query_shippable函数中检测bitmap确认是否能ship。exec_nodes中记录的最重要的信息就是需要在哪个节点上执行由pgxc_FQS_find_datanodes函数计算出来。计算逻辑 exec_nodes pgxc_is_query_shippable(query, 0);if (exec_nodes NULL)return NULL;glob makeNode(PlannerGlobal);glob-boundParams boundParams;root makeNode(PlannerInfo);root-parse query;root-glob glob;root-query_level 1;root-planner_cxt CurrentMemoryContext;top_plan (Plan *)pgxc_FQS_create_remote_plan(query, exec_nodes, false);top_plan set_plan_references(root, top_plan);result makeNode(PlannedStmt);result-commandType query-commandType;result-canSetTag query-canSetTag;result-utilityStmt query-utilityStmt;if (query-commandType ! CMD_SELECT)result-resultRelations list_make1_int(query-resultRelation);result-planTree top_plan;result-rtable query-rtable;result-queryId query-queryId;result-relationOids glob-relationOids;result-invalItems glob-invalItems;return result;
}FQS的计划会比较简单基本就是把SQL用deparse_query出来然后拼到计划节点中找到发到哪些节点执行即可。
2.2 standard_planner生成remote计划
回到行锁用例上
drop table TBL_33;
create table TBL_33(c33 int);
insert into TBL_33 values(0);SELECT c33 FROM TBL_33 WHERE c330 for update;分布式执行计划
explain SELECT c33 FROM TBL_33 WHERE c330 for update;QUERY PLAN
-------------------------------------------------------------------------------Remote Subquery Scan on all (datanode_2) (cost0.00..42.01 rows13 width10)- LockRows (cost0.00..42.01 rows13 width10)- Seq Scan on tbl_33 (cost0.00..41.88 rows13 width10)Filter: (c33 0)2.2.1 subquery_planner→grouping_planner生成local计划
subquery_planner生成计划
2.2.2 make_remotesubplan为计划添加remote算子
standard_planner → make_remotesubplan
standard_planner...best_path get_cheapest_fractional_path(final_rel, tuple_fraction);if (!root-distribution)root-distribution best_path-distribution;top_plan create_plan(root, best_path);if (root-distribution)top_plan (Plan *) make_remotesubplan(root, top_plan, NULL, root-distribution, root-sort_pathkeys);2.2.3 path的distribution信息从哪来
explain SELECT c33 FROM TBL_33 WHERE c330 for update;QUERY PLAN
-------------------------------------------------------------------------------Remote Subquery Scan on all (datanode_2) (cost0.00..42.01 rows13 width10)- LockRows (cost0.00..42.01 rows13 width10)- Seq Scan on tbl_33 (cost0.00..41.88 rows13 width10)Filter: (c33 0)SELECT c33 FROM TBL_33 WHERE c330 for update;执行时会生成两个算子
create_seqscan_pathcreate_lockrows_path
create_seqscan_path
Path *
create_seqscan_path(PlannerInfo *root, RelOptInfo *rel,Relids required_outer, int parallel_workers)
{Path *pathnode makeNode(Path);pathnode-pathtype T_SeqScan;pathnode-parent rel;pathnode-pathtarget rel-reltarget;pathnode-param_info get_baserel_parampathinfo(root, rel,required_outer);pathnode-parallel_aware parallel_workers 0 ? true : false;pathnode-parallel_safe rel-consider_parallel;pathnode-parallel_workers parallel_workers;pathnode-pathkeys NIL; /* seqscan has unordered result */#ifdef XCPset_scanpath_distribution会配置pathnode-distribution信息标记计划需要发到哪个节点执行。restrict_distribution会更严格的检查计划发到哪个节点。 set_scanpath_distribution(root, rel, pathnode);if (rel-baserestrictinfo){ListCell *lc;foreach (lc, rel-baserestrictinfo){RestrictInfo *ri (RestrictInfo *) lfirst(lc);restrict_distribution(root, ri, pathnode);}}
#endifcost_seqscan(pathnode, root, rel, pathnode-param_info);return pathnode;
}
经过set_scanpath_distribution后 pathnode-distribution-nodes标记了dn0、dn1。p/t pathnode-distribution-nodes-words[0] 11 经过restrict_distribution后 pathnode-distribution-nodesrestrictNodes只标记了datanode1。p/t pathnode-distribution-restrictNodes-words[0] 10
p *pathnode-distribution
$27 {type T_Distribution, distributionType 72 H, distributionExpr 0x135fea8, nodes 0x1360650, restrictNodes 0x1360898}
(gdb) p/t pathnode-distribution-nodes-words[0]
$31 11
(gdb) p/t pathnode-distribution-restrictNodes-words[0]
$30 10create_lockrows_path
lockrows节点比较特殊不需要做什么事情执行器会在执行阶段特殊处理。pathnode→distribution信息集成subplan的即可。
LockRowsPath *
create_lockrows_path(PlannerInfo *root, RelOptInfo *rel,Path *subpath, List *rowMarks, int epqParam)
{LockRowsPath *pathnode makeNode(LockRowsPath);pathnode-path.pathtype T_LockRows;...... pathnode-path.distribution copyObject(subpath-distribution);......return pathnode;
}
