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商场网页的浏览量升高了107,源码解读

日期:2019-10-05编辑作者:必赢网上注册

PG 11将在正式布告,本节轻易了PG 11的部分新特点,富含互相查询的性子进步和多少表分区的效能加强。

HTTP公约是前者质量以致安全中贰个拾分首要的话题,前段时间在看《web质量权威指南(High Performance Browser Networking)》,把里面有关HTTP部分的源委拿出来分享一下,加了一些温馨的主见,当然未有《HTTP权威指南》讲得详细,但对于精晓我们平常做的政工很有启迪。猜度会有两三篇小说,珍视分别会涉及到HTTP 1.1、HTTPS、HTTP 2.0等剧情,本篇主要涉及HTTP 1.1会同使用。

原先的章节已介绍了函数query_planner中子函数remove_useless_joins、reduce_unique_semijoins和add_placeholders_to_base_rels的要害完毕逻辑,本节继续介绍create_lateral_join_info、match_foreign_keys_to_quals和extract_restriction_or_clauses的兑现逻辑。

架构师是二个充满挑衅的营生,知识面包车型客车宽窄往往调节着一个架构师的架构技能

单例对象(Singleton)是一种常用的设计格局。在Java应用中,单例对象能确保在三个JVM中,该指标独有一个实例存在。那样的格局有多少个实惠:

一、并行查询

Parallel HashHash Join奉行时,在结构Hash表和实行Hash连接时,PG 11可应用并行的方法实践。测量检验脚本:

testdb=# create table t1 (c1 int,c2 varchar,c3 varchar;CREATE TABLEtestdb=# testdb=# insert into t1 select generate_series(1,5000000),'TEST'||generate_series(1,1000000),generate_series(1,1000000)||'TEST';INSERT 0 5000000testdb=# drop table if exists t2;DROP TABLEtestdb=# create table t2 (c1 int,c2 varchar,c3 varchar;CREATE TABLEtestdb=# testdb=# insert into t2 select generate_series(1,1000000),'T2'||generate_series(1,1000000),generate_series(1,1000000)||'T2';INSERT 0 1000000testdb=# explain verbosetestdb-# select t1.c1,t2.c1 testdb-# from t1 inner join t2 on t1.c1 = t2.c1; QUERY PLAN --------------------------------------------------------------------------------------------- Gather (cost=18372.00..107975.86 rows=101100 width=8) Output: t1.c1, t2.c1 Workers Planned: 2 -- 2 Workers -> Parallel Hash Join (cost=17372.00..96865.86 rows=42125 width=8) -- Parallel Hash Join Output: t1.c1, t2.c1 Hash Cond: (t1.c1 = t2.c1) -> Parallel Seq Scan on public.t1 (cost=0.00..45787.33 rows=2083333 width=4) Output: t1.c1 -> Parallel Hash (cost=10535.67..10535.67 rows=416667 width=4) -- Parallel Hash Output: t2.c1 -> Parallel Seq Scan on public.t2 (cost=0.00..10535.67 rows=416667 width=4) Output: t2.c1

除此之外Parallel Hash外,PG 11在进行Parallel Append(试行UNION ALL等聚焦操作)/CREATE TABLE AS SELECT/CREATE MATE本田CR-VIALIZED VIEW/SELECT INTO/CREATE INDEX等操作时以互相的艺术实践.

HTTP 0.9

HTTP的第三个本子被官方称为HTTP0.9,那是个只有一行的说道,举个例子:

GET /about/

HTTP 0.9有多少个要点:

  • 客商端/服务器、需要/响应公约
  • 商场网页的浏览量升高了107,源码解读。ASCII 商业事务,运营于TCP/IP链接之上
  • 统一筹算用来传输超文本文档
  • 服务器与顾客端之间的连年在历次恳求之后都会关闭

本条版本的HTTP主要用来传输文本,並且未有共用TCP连接。

query_planner代码片段:

因为未来是多个音讯时代,大批量的新闻都以要求仓库储存并索求的,数据库设计的倒霉,将会严重影响系统的天性,而那点往往会被我们的陈设性人员大体,他们只略知一二服从那么些范式而不会结合数据的特点去规划数据库。

  1. 或多或少类创造相比较频仍,对于一些特大型的对象,那是一笔异常的大的系统开采。

  2. 节约了new操作符,减弱了系统内部存款和储蓄器的使用频率,缓慢消除GC压力。

  3. 有些类如交易所的着力交易引擎,调整着交易流程,尽管此类能够创制七个的话,系统完全乱了。(举例三个军事出现了五个上校同有的时候候指挥,肯定会乱成一团),所以唯有选取单例方式,技能有限支撑中央交易服务器独立垄断(monopoly)总体流程。

二、数据表分区

Hash PartitionPG 在11.x引进了Hash分区,关于Hash分区,官方文档有如下表明:

The table is partitioned by specifying a modulus and a remainder for each partition. Each partition will hold the rows for which the hash value of the partition key divided by the specified modulus will produce the specified remainder.

每一个Hash分区需点名"模"和"余"(remainder),数据在哪些分区(partition index)的计算公式:partition index = abs(hashfunc % modulus

drop table if exists t_hash1;create table t_hash1 (c1 int,c2 varchar,c3 varchar partition by hash;create table t_hash1_1 partition of t_hash1 for values with (modulus 6,remainder 0);create table t_hash1_2 partition of t_hash1 for values with (modulus 6,remainder 1);create table t_hash1_3 partition of t_hash1 for values with (modulus 6,remainder 2);create table t_hash1_4 partition of t_hash1 for values with (modulus 6,remainder 3);create table t_hash1_5 partition of t_hash1 for values with (modulus 6,remainder 4);create table t_hash1_6 partition of t_hash1 for values with (modulus 6,remainder 5);testdb=# insert into t_hash1 testdb-# select generate_series(1,1000000),'HASH'||generate_series(1,1000000),generate_series(1,1000000)||'HASH';INSERT 0 1000000

多少在各分区上的遍及大概均匀.2018-9-19 注:由于插入数据时语句出错,前日得出的结果有误(但数目在相继分区的分布上不太均匀,t_hash1_1分区行数鲜明的比其余分区的要多浩大),请忽略

testdb=# select count from only t_hash1;; count ------- 0testdb=# select count from only t_hash1_1; count -------- 166480testdb=# select count from only t_hash1_2; count -------- 166904testdb=# select count from only t_hash1_3; count -------- 166302testdb=# select count from only t_hash1_4; count -------- 166783testdb=# select count from only t_hash1_5; count -------- 166593testdb=# select count from only t_hash1_6; count -------- 166938

Hash分区键亦能够创制在字符型字段上

testdb=# drop table if exists t_hash3;DROP TABLEtestdb=# create table t_hash3 (c1 int,c2 varchar,c3 varchar partition by hash;CREATE TABLE-- 需创建相应的"Partition"用于存储相应的数据testdb=# insert into t_hash3 testdb-# select generate_series,'HASH'||generate_series(1,1000000),generate_series(1,1000000)||'HASH';ERROR: no partition of relation "t_hash3" found for rowDETAIL: Partition key of the failing row contains  = .-- 6个分区,3个sub-table,插入数据会出错testdb=# testdb=# create table t_hash3_1 partition of t_hash3 for values with (modulus 6,remainder 0);CREATE TABLEtestdb=# create table t_hash3_2 partition of t_hash3 for values with (modulus 6,remainder 1);CREATE TABLEtestdb=# create table t_hash3_3 partition of t_hash3 for values with (modulus 6,remainder 2);CREATE TABLEtestdb=# insert into t_hash3 testdb-# select generate_series,'HASH'||generate_series,generate_series||'HASH';ERROR: no partition of relation "t_hash3" found for rowDETAIL: Partition key of the failing row contains  = .-- 3个分区,3个sub-table,正常testdb=# drop table if exists t_hash3;DROP TABLEtestdb=# create table t_hash3 (c1 int,c2 varchar,c3 varchar partition by hash;CREATE TABLEtestdb=# create table t_hash3_1 partition of t_hash3 for values with (modulus 3,remainder 0);CREATE TABLEtestdb=# create table t_hash3_2 partition of t_hash3 for values with (modulus 3,remainder 1);CREATE TABLEtestdb=# create table t_hash3_3 partition of t_hash3 for values with (modulus 3,remainder 2);CREATE TABLEtestdb=# insert into t_hash3 testdb-# select generate_series,'HASH'||generate_series,generate_series||'HASH';INSERT 0 10000

观测分区的数据布满,还相比较均匀:

testdb=# testdb=# select count from only t_hash3; count ------- 0testdb=# select count from only t_hash3_1; count ------- 3378testdb=# select count from only t_hash3_2; count ------- 3288testdb=# select count from only t_hash3_3; count ------- 3334

Default PartitionList和Range分区可内定Default Partition(Hash分区不辅助).

Update partition keyPG 11可Update分区键,那会导致数据的"迁移".

bwin手机版客户端,Create unique constraintPG 11在分区表上创办主键和独一索引(注:Oracle在很早的本子已帮衬此本性).在平日字段上能够成立BTree索引.

testdb=# alter table t_hash1 add primary key;ALTER TABLEtestdb=# create index idx_t_hash1_c2 on t_hash1;CREATE INDEX

FOREIGN KEY supportPG 11支撑在分区上创办外键.

除去上述多少个新特点外,分区上边,PG 11在Automatic index creation/INSERT ON CONFLICT/Partition-Wise Join / Partition-Wise Aggregate/FOEscort EACH ROW trigger/Dynamic Partition Elimination/Control Partition Pruning上均具有加强.

HTTP 1.0

贰个首屈一指的HTTP 1.0呼吁进度如下:

GET /rfc/rfc1945.txt HTTP/1.0 User-Agent: CERN-LineMode/2.15 libwww/2.17b3 Accept: */* HTTP/1.0 200 OK Content-Type: text/plain Content-Length: 137582Expires: Thu, 01 Dec 1997 16:00:00 GMT Last-Modified: Wed, 1 May 1996 12:45:26 GMT Server: Apache 0.84

绝对前二个本子,HTTP 1.0第一有以下几点变化:

  • 伸手和相应能够由于多行首部字段构成
  • 一呼百应对象前面增多了一个响应状态
  • 响应对象不局限于超文本
  • 服务器与客户端之间的连接在历次须求之后都会关闭
  • 落实了Expires等传输内容的缓存控制
  • 内容编码Accept-Encoding、字符集Accept-Charset等公约内容的辅助

此时最早有了央浼及重临首部的概念,伊始传输不限于文本

 //... /* * Construct the lateral reference sets now that we have finalized * PlaceHolderVar eval levels. */ create_lateral_join_info;//创建Lateral连接信息 /* * Match foreign keys to equivalence classes and join quals. This must be * done after finalizing equivalence classes, and it's useful to wait till * after join removal so that we can skip processing foreign keys * involving removed relations. */ match_foreign_keys_to_quals;//匹配外键信息 /* * Look for join OR clauses that we can extract single-relation * restriction OR clauses from. */ extract_restriction_or_clauses;//在OR语句中抽取约束条件 /* * We should now have size estimates for every actual table involved in * the query, and we also know which if any have been deleted from the * query by join removal; so we can compute total_table_pages. * * Note that appendrels are not double-counted here, even though we don't * bother to distinguish RelOptInfos for appendrel parents, because the * parents will still have size zero. * * XXX if a table is self-joined, we will count it once per appearance, * which perhaps is the wrong thing ... but that's not completely clear, * and detecting self-joins here is difficult, so ignore it for now. */ total_pages = 0; for (rti = 1; rti < root->simple_rel_array_size; rti++)//计算总pages { RelOptInfo *brel = root->simple_rel_array[rti]; if (brel == NULL) continue; Assert(brel->relid == rti); /* sanity check on array */ if (IS_SIMPLE_REL total_pages +=  brel->pages; } root->total_table_pages = total_pages;//赋值 //...

从贰个技术员到架构师是三个十分的大的转移,架构师须要从大的上边思虑,而不只是思索这几个模块该用哪类设计情势去开垦。

单例形式可以分成懒汉式饿汉式

三、参谋资料

PostgreSQL 11 New Features With ExamplesPostgreSQL 11 Table Partitioning

HTTP 1.1

HTTP 1.1是当下当先1/2选拔所利用的商业事务版本。相对前面包车型地铁1.0本子,HTTP 1.1语义格式基本维持不变,然而它参预了繁多首要的质量优化:持久连接、分块编码传输、字节范围诉求、巩固的缓存机制、传输编码及诉求管道

实则,长久链接在新生被反向移植到了HTTP1.0上

一、数据结构

RelOptInfoRelOptInfo中,与LATERAL相关的数据结构

 typedef struct RelOptInfo { NodeTag type;//节点标识 RelOptKind reloptkind;//RelOpt类型 //... /* parameterization information needed for both base rels and join rels */ /* (see also lateral_vars and lateral_referencers) */ Relids direct_lateral_relids; /*使用lateral语法,需依赖的Relids rels directly laterally referenced */ Relids lateral_relids; /* minimum parameterization of rel */ //... List *lateral_vars; /* 关系依赖的Vars/PHVs LATERAL Vars and PHVs referenced by rel */ Relids lateral_referencers; /*依赖该关系的Relids rels that reference me laterally */ //... } RelOptInfo;

不问可见,想要成为架构师,要求有耐心,不断学习,拓展自个儿的视界,不止局限于本身眼下的花色

  • 懒汉式单例格局:在类加载时不开始化。
  • 饿汉式单例情势:在类加载时就成功了早先化,所以类加载非常的慢,但收获对象的速度快。

HTTP 2.0

HTTP 2.0 的关键对象是创新传输品质,实现低顺延和高吞吐量。HTTP 2.0作了不菲属性角度的优化,另一方面,HTTP的高层磋商语义并不会因为此次版本进级而受影响。全体HTTP首部、值,以及它们的应用处境都不会变。现存的别的网址和利用,无需做任何修改都能够在 HTTP 2.0 上跑起来。换句话说, 等之后大家的服务器、客商端都补助HTTP 2.0的时候,大家绝不为了利用 HTTP 2.0 的好处而修改标识,作过多外加的编码,却能共享到它带动的更低的推迟和更加高的互联网连接利用率交付!

HTTP 2.0的原委将要下篇或下下篇放出,本文不对其做过多润色

近些日子讲到,HTTP 1.1这几个本子引进了大气抓牢品质的首要特色,个中富含:

  • 持久化连接以协助连接重用
  • 分块传输编码以支撑流式响应
  • 伸手管道以支撑相互央求管理
  • 字节服务以协助基于范围的财富央浼
  • 创新的更加好的缓存机制

此地最首要讲一下长久化、管道在前端品质优化中的一些使用

二、源码解读

create_lateral_join_infoPG在提供LATERAL语法此前,假定全体的子查询都得以单独存在,不可能相互引用属性只怕引用上层的习性,为了能够引用别的或上层的属性,必要在子查询前边显式钦点LATERAL关键字.举个例子以下的SQL语句,不显式钦命LATERAL关键字不可能平常运营:

testdb=# select a.*,b.grbh,b.je testdb-# from t_dwxx a,(select t1.dwbh,t1.grbh,t2.je from t_grxx t1 inner join t_jfxx t2 on t1.dwbh = a.dwbh and t1.grbh = t2.grbh) btestdb-# where a.dwbh = '1001'testdb-# order by b.dwbh;ERROR: invalid reference to FROM-clause entry for table "a"LINE 2: ... from t_grxx t1 inner join t_jfxx t2 on t1.dwbh = a.dwbh and... ^HINT: There is an entry for table "a", but it cannot be referenced from this part of the query.

在子查询前显式钦点LATERAL后,可以健康运作:

testdb=# select a.*,b.grbh,b.je testdb-# from t_dwxx a,lateral (select t1.dwbh,t1.grbh,t2.je from t_grxx t1 inner join t_jfxx t2 on t1.dwbh = a.dwbh and t1.grbh = t2.grbh) btestdb-# where a.dwbh = '1001'testdb-# order by b.dwbh; dwmc | dwbh | dwdz | grbh | je -----------+------+--------------------+------+------- X有限公司 | 1001 | 广东省广州市荔湾区 | 901 | 401.3 X有限公司 | 1001 | 广东省广州市荔湾区 | 901 | 401.3 X有限公司 | 1001 | 广东省广州市荔湾区 | 901 | 401.3

如函数注释所叙述的,create_lateral_join_info函数的意义是填充RelOptInfo中的连带四个变量,"Fill in the per-base-relation direct_lateral_relids, lateral_relids和and lateral_referencers sets"

源代码如下:

 /* * create_lateral_join_info * Fill in the per-base-relation direct_lateral_relids, lateral_relids * and lateral_referencers sets. * * This has to run after deconstruct_jointree, because we need to know the * final ph_eval_at values for PlaceHolderVars. */ void create_lateral_join_info(PlannerInfo *root) { bool found_laterals = false; Index rti; ListCell *lc; /* We need do nothing if the query contains no LATERAL RTEs */ if (!root->hasLateralRTEs)//是否存在LateralRTE return; /* * Examine all baserels (the rel array has been set up by now). */ for (rti = 1; rti < root->simple_rel_array_size; rti++)//遍历 { RelOptInfo *brel = root->simple_rel_array[rti]; Relids lateral_relids; /* there may be empty slots corresponding to non-baserel RTEs */ if (brel == NULL) continue; Assert(brel->relid == rti); /* sanity check on array */ /* ignore RTEs that are "other rels" */ if (brel->reloptkind != RELOPT_BASEREL) continue; lateral_relids = NULL; /* consider each laterally-referenced Var or PHV */ foreach(lc, brel->lateral_vars) { Node *node =  lfirst; if (IsA(node, Var)) { Var *var =  node; found_laterals = true; lateral_relids = bms_add_member(lateral_relids, var->varno); } else if (IsA(node, PlaceHolderVar)) { PlaceHolderVar *phv = (PlaceHolderVar *) node; PlaceHolderInfo *phinfo = find_placeholder_info(root, phv, false); found_laterals = true; lateral_relids = bms_add_members(lateral_relids, phinfo->ph_eval_at); } else Assert; } /* We now have all the simple lateral refs from this rel */ brel->direct_lateral_relids = lateral_relids; brel->lateral_relids = bms_copy(lateral_relids); } /* * Now check for lateral references within PlaceHolderVars, and mark their * eval_at rels as having lateral references to the source rels. * * For a PHV that is due to be evaluated at a baserel, mark its source * as direct lateral dependencies of the baserel (adding onto the ones * recorded above). If it's due to be evaluated at a join, mark its * source as indirect lateral dependencies of each baserel in the join, * ie put them into lateral_relids but not direct_lateral_relids. This is * appropriate because we can't put any such baserel on the outside of a * join to one of the PHV's lateral dependencies, but on the other hand we * also can't yet join it directly to the dependency. */ foreach(lc, root->placeholder_list) { PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst; Relids eval_at = phinfo->ph_eval_at; int varno; if (phinfo->ph_lateral == NULL) continue; /* PHV is uninteresting if no lateral refs */ found_laterals = true; if (bms_get_singleton_member(eval_at, &varno)) { /* Evaluation site is a baserel */ RelOptInfo *brel = find_base_rel(root, varno); brel->direct_lateral_relids = bms_add_members(brel->direct_lateral_relids, phinfo->ph_lateral); brel->lateral_relids = bms_add_members(brel->lateral_relids, phinfo->ph_lateral); } else { /* Evaluation site is a join */ varno = -1; while ((varno = bms_next_member(eval_at, varno)) >= 0) { RelOptInfo *brel = find_base_rel(root, varno); brel->lateral_relids = bms_add_members(brel->lateral_relids, phinfo->ph_lateral); } } } /* * If we found no actual lateral references, we're done; but reset the * hasLateralRTEs flag to avoid useless work later. */ if (!found_laterals) { root->hasLateralRTEs = false; return; } /* * Calculate the transitive closure of the lateral_relids sets, so that * they describe both direct and indirect lateral references. If relation * X references Y laterally, and Y references Z laterally, then we will * have to scan X on the inside of a nestloop with Z, so for all intents * and purposes X is laterally dependent on Z too. * * This code is essentially Warshall's algorithm for transitive closure. * The outer loop considers each baserel, and propagates its lateral * dependencies to those baserels that have a lateral dependency on it. */ for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *brel = root->simple_rel_array[rti]; Relids outer_lateral_relids; Index rti2; if (brel == NULL || brel->reloptkind != RELOPT_BASEREL) continue; /* need not consider baserel further if it has no lateral refs */ outer_lateral_relids = brel->lateral_relids; if (outer_lateral_relids == NULL) continue; /* else scan all baserels */ for (rti2 = 1; rti2 < root->simple_rel_array_size; rti2++) { RelOptInfo *brel2 = root->simple_rel_array[rti2]; if (brel2 == NULL || brel2->reloptkind != RELOPT_BASEREL) continue; /* if brel2 has lateral ref to brel, propagate brel's refs */ if (bms_is_member(rti, brel2->lateral_relids)) brel2->lateral_relids = bms_add_members(brel2->lateral_relids, outer_lateral_relids); } } /* * Now that we've identified all lateral references, mark each baserel * with the set of relids of rels that reference it laterally (possibly * indirectly) --- that is, the inverse mapping of lateral_relids. */ for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *brel = root->simple_rel_array[rti]; Relids lateral_relids; int rti2; if (brel == NULL || brel->reloptkind != RELOPT_BASEREL) continue; /* Nothing to do at rels with no lateral refs */ lateral_relids = brel->lateral_relids; if (lateral_relids == NULL) continue; /* * We should not have broken the invariant that lateral_relids is * exactly NULL if empty. */ Assert(!bms_is_empty(lateral_relids)); /* Also, no rel should have a lateral dependency on itself */ Assert(!bms_is_member(rti, lateral_relids)); /* Mark this rel's referencees */ rti2 = -1; while ((rti2 = bms_next_member(lateral_relids, rti2)) >= 0) { RelOptInfo *brel2 = root->simple_rel_array[rti2]; Assert(brel2 != NULL && brel2->reloptkind == RELOPT_BASEREL); brel2->lateral_referencers = bms_add_member(brel2->lateral_referencers, rti); } } /* * Lastly, propagate lateral_relids and lateral_referencers from appendrel * parent rels to their child rels. We intentionally give each child rel * the same minimum parameterization, even though it's quite possible that * some don't reference all the lateral rels. This is because any append * path for the parent will have to have the same parameterization for * every child anyway, and there's no value in forcing extra * reparameterize_path() calls. Similarly, a lateral reference to the * parent prevents use of otherwise-movable join rels for each child. */ for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *brel = root->simple_rel_array[rti]; RangeTblEntry *brte = root->simple_rte_array[rti]; /* * Skip empty slots. Also skip non-simple relations i.e. dead * relations. */ if (brel == NULL || !IS_SIMPLE_REL continue; /* * In the case of table inheritance, the parent RTE is directly linked * to every child table via an AppendRelInfo. In the case of table * partitioning, the inheritance hierarchy is expanded one level at a * time rather than flattened. Therefore, an other member rel that is * a partitioned table may have children of its own, and must * therefore be marked with the appropriate lateral info so that those * children eventually get marked also. */ Assert; if (brel->reloptkind == RELOPT_OTHER_MEMBER_REL && (brte->rtekind != RTE_RELATION || brte->relkind != RELKIND_PARTITIONED_TABLE)) continue; if (brte->inh) { foreach(lc, root->append_rel_list) { AppendRelInfo *appinfo = (AppendRelInfo *) lfirst; RelOptInfo *childrel; if (appinfo->parent_relid != rti) continue; childrel = root->simple_rel_array[appinfo->child_relid]; Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL); Assert(childrel->direct_lateral_relids == NULL); childrel->direct_lateral_relids = brel->direct_lateral_relids; Assert(childrel->lateral_relids == NULL); childrel->lateral_relids = brel->lateral_relids; Assert(childrel->lateral_referencers == NULL); childrel->lateral_referencers = brel->lateral_referencers; } } } }

盯住深入分析:

 b planmain.c:173Breakpoint 1 at 0x76961a: file planmain.c, line 173. cContinuing.Breakpoint 1, query_planner (root=0x1702b80, tlist=0x174a870, qp_callback=0x76e97d <standard_qp_callback>, qp_extra=0x7ffd35e059c0) at planmain.c:177... 212 create_lateral_join_info;

查看root变量:

 p *root$11 = {..., hasLateralRTEs = false, ...}

通过管理后,LATERAL已经无影无踪(hasLateralRTEs = false),无需实行管理.

match_foreign_keys_to_quals这是外键相关的拍卖,等价类与外键约束进行相称并出席到基准语句中

 /* * match_foreign_keys_to_quals * Match foreign-key constraints to equivalence classes and join quals * * The idea here is to see which query join conditions match equality * constraints of a foreign-key relationship. For such join conditions, * we can use the FK semantics to make selectivity estimates that are more * reliable than estimating from statistics, especially for multiple-column * FKs, where the normal assumption of independent conditions tends to fail. * * In this function we annotate the ForeignKeyOptInfos in root->fkey_list * with info about which eclasses and join qual clauses they match, and * discard any ForeignKeyOptInfos that are irrelevant for the query. */ void match_foreign_keys_to_quals(PlannerInfo *root) { List *newlist = NIL; ListCell *lc; foreach(lc, root->fkey_list) { ForeignKeyOptInfo *fkinfo = (ForeignKeyOptInfo *) lfirst; RelOptInfo *con_rel; RelOptInfo *ref_rel; int colno; /* * Either relid might identify a rel that is in the query's rtable but * isn't referenced by the jointree so won't have a RelOptInfo. Hence * don't use find_base_rel() here. We can ignore such FKs. */ if (fkinfo->con_relid >= root->simple_rel_array_size || fkinfo->ref_relid >= root->simple_rel_array_size) continue; /* just paranoia */ con_rel = root->simple_rel_array[fkinfo->con_relid]; if (con_rel == NULL) continue; ref_rel = root->simple_rel_array[fkinfo->ref_relid]; if (ref_rel == NULL) continue; /* * Ignore FK unless both rels are baserels. This gets rid of FKs that * link to inheritance child rels (otherrels) and those that link to * rels removed by join removal (dead rels). */ if (con_rel->reloptkind != RELOPT_BASEREL || ref_rel->reloptkind != RELOPT_BASEREL) continue; /* * Scan the columns and try to match them to eclasses and quals. * * Note: for simple inner joins, any match should be in an eclass. * "Loose" quals that syntactically match an FK equality must have * been rejected for EC status because they are outer-join quals or * similar. We can still consider them to match the FK if they are * not outerjoin_delayed. */ for (colno = 0; colno < fkinfo->nkeys; colno++) { AttrNumber con_attno, ref_attno; Oid fpeqop; ListCell *lc2; fkinfo->eclass[colno] = match_eclasses_to_foreign_key_col(root, fkinfo, colno); /* Don't bother looking for loose quals if we got an EC match */ if (fkinfo->eclass[colno] != NULL) { fkinfo->nmatched_ec++; continue; } /* * Scan joininfo list for relevant clauses. Either rel's joininfo * list would do equally well; we use con_rel's. */ con_attno = fkinfo->conkey[colno]; ref_attno = fkinfo->confkey[colno]; fpeqop = InvalidOid; /* we'll look this up only if needed */ foreach(lc2, con_rel->joininfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst; OpExpr *clause =  rinfo->clause; Var *leftvar; Var *rightvar; /* Ignore outerjoin-delayed clauses */ if (rinfo->outerjoin_delayed) continue; /* Only binary OpExprs are useful for consideration */ if (!IsA(clause, OpExpr) || list_length(clause->args) != 2) continue; leftvar =  get_leftop clause); rightvar =  get_rightop clause); /* Operands must be Vars, possibly with RelabelType */ while (leftvar && IsA(leftvar, RelabelType)) leftvar =  ((RelabelType *) leftvar)->arg; if (!(leftvar && IsA(leftvar, Var))) continue; while (rightvar && IsA(rightvar, RelabelType)) rightvar =  ((RelabelType *) rightvar)->arg; if (!(rightvar && IsA(rightvar, Var))) continue; /* Now try to match the vars to the current foreign key cols */ if (fkinfo->ref_relid == leftvar->varno && ref_attno == leftvar->varattno && fkinfo->con_relid == rightvar->varno && con_attno == rightvar->varattno) { /* Vars match, but is it the right operator? */ if (clause->opno == fkinfo->conpfeqop[colno]) { fkinfo->rinfos[colno] = lappend(fkinfo->rinfos[colno], rinfo); fkinfo->nmatched_ri++; } } else if (fkinfo->ref_relid == rightvar->varno && ref_attno == rightvar->varattno && fkinfo->con_relid == leftvar->varno && con_attno == leftvar->varattno) { /* * Reverse match, must check commutator operator. Look it * up if we didn't already. (In the worst case we might * do multiple lookups here, but that would require an FK * equality operator without commutator, which is * unlikely.) */ if (!OidIsValid fpeqop = get_commutator(fkinfo->conpfeqop[colno]); if (clause->opno == fpeqop) { fkinfo->rinfos[colno] = lappend(fkinfo->rinfos[colno], rinfo); fkinfo->nmatched_ri++; } } } /* If we found any matching loose quals, count col as matched */ if (fkinfo->rinfos[colno]) fkinfo->nmatched_rcols++; } /* * Currently, we drop multicolumn FKs that aren't fully matched to the * query. Later we might figure out how to derive some sort of * estimate from them, in which case this test should be weakened to * "if ((fkinfo->nmatched_ec + fkinfo->nmatched_rcols) > 0)". */ if ((fkinfo->nmatched_ec + fkinfo->nmatched_rcols) == fkinfo->nkeys) newlist = lappend(newlist, fkinfo); } /* Replace fkey_list, thereby discarding any useless entries */ root->fkey_list = newlist; }

extract_restriction_or_clauses反省join连接条件的OR-of-AND语句,如存在有用的O奥迪Q3约束标准,则提收取来.如代码注释所描述,((a.x = 42 AND b.y = 43) O昂Cora (a.x = 44 AND b.z = 45)),能够领到条件(a.x = 42 OR a.x = 44) AND (b.y = 43 O奇骏 b.z = 45),提取那一个准绳的指标是为了在连接前能把这么些条件下推到关系中,减少参加连接运算的元组数量.举个例子:

testdb=# explain verbose select t1.*from t_dwxx t1 inner join t_grxx t2 on (t1.dwbh = '1001' and t2.grbh = '901') OR (t1.dwbh = '1002' and t2.grbh = '902'); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------- Nested Loop (cost=0.00..17.23 rows=5 width=474) Output: t1.dwmc, t1.dwbh, t1.dwdz Join Filter: ((::text = '1001'::text) AND ::text = '901'::text)) OR (::text = '1002'::text) AND ::text = '902'::text))) -> Seq Scan on public.t_grxx t2 (cost=0.00..16.00 rows=4 width=38) Output: t2.dwbh, t2.grbh, t2.xm, t2.xb, t2.nl Filter: (::text = '901'::text) OR ::text = '902'::text)) -> Materialize (cost=0.00..1.05 rows=2 width=474) Output: t1.dwmc, t1.dwbh, t1.dwdz -> Seq Scan on public.t_dwxx t1 (cost=0.00..1.04 rows=2 width=474) Output: t1.dwmc, t1.dwbh, t1.dwdz Filter: (::text = '1001'::text) OR ::text = '1002'::text))

能够看出,t1.dwbh = '1001' O劲客 t1.dwbh = '1002'和t2.grbh = '901' OPRADOt2.grbh = '902'在一连前下推到数量表扫描作为过滤条件.

 /* * extract_restriction_or_clauses * Examine join OR-of-AND clauses to see if any useful restriction OR * clauses can be extracted. If so, add them to the query. * * Although a join clause must reference multiple relations overall, * an OR of ANDs clause might contain sub-clauses that reference just one * relation and can be used to build a restriction clause for that rel. * For example consider * WHERE ((a.x = 42 AND b.y = 43) OR (a.x = 44 AND b.z = 45)); * We can transform this into * WHERE ((a.x = 42 AND b.y = 43) OR (a.x = 44 AND b.z = 45)) * AND (a.x = 42 OR a.x = 44) * AND (b.y = 43 OR b.z = 45); * which allows the latter clauses to be applied during the scans of a and b, * perhaps as index qualifications, and in any case reducing the number of * rows arriving at the join. In essence this is a partial transformation to * CNF (AND of ORs format). It is not complete, however, because we do not * unravel the original OR --- doing so would usually bloat the qualification * expression to little gain. * * The added quals are partially redundant with the original OR, and therefore * would cause the size of the joinrel to be underestimated when it is finally * formed. (This would be true of a full transformation to CNF as well; the * fault is not really in the transformation, but in clauselist_selectivity's * inability to recognize redundant conditions.) We can compensate for this * redundancy by changing the cached selectivity of the original OR clause, * canceling out the  reduction in the estimated sizes of the base * relations so that the estimated joinrel size remains the same. This is * a MAJOR HACK: it depends on the fact that clause selectivities are cached * and on the fact that the same RestrictInfo node will appear in every * joininfo list that might be used when the joinrel is formed. * And it doesn't work in cases where the size estimation is nonlinear * (i.e., outer and IN joins). But it beats not doing anything. * * We examine each base relation to see if join clauses associated with it * contain extractable restriction conditions. If so, add those conditions * to the rel's baserestrictinfo and update the cached selectivities of the * join clauses. Note that the same join clause will be examined afresh * from the point of view of each baserel that participates in it, so its * cached selectivity may get updated multiple times. */ void extract_restriction_or_clauses(PlannerInfo *root) { Index rti; /* Examine each baserel for potential join OR clauses */ for (rti = 1; rti < root->simple_rel_array_size; rti++) { RelOptInfo *rel = root->simple_rel_array[rti]; ListCell *lc; /* there may be empty slots corresponding to non-baserel RTEs */ if (rel == NULL) continue; Assert(rel->relid == rti); /* sanity check on array */ /* ignore RTEs that are "other rels" */ if (rel->reloptkind != RELOPT_BASEREL) continue; /* * Find potentially interesting OR joinclauses. We can use any * joinclause that is considered safe to move to this rel by the * parameterized-path machinery, even though what we are going to do * with it is not exactly a parameterized path. * * However, it seems best to ignore clauses that have been marked * redundant (by setting norm_selec > 1). That likely can't happen * for OR clauses, but let's be safe. */ foreach(lc, rel->joininfo) { RestrictInfo *rinfo = (RestrictInfo *) lfirst; if (restriction_is_or_clause && join_clause_is_movable_to(rinfo, rel) && rinfo->norm_selec <= 1) { /* Try to extract a qual for this rel only */ Expr *orclause = extract_or_clause(rinfo, rel); /* * If successful, decide whether we want to use the clause, * and insert it into the rel's restrictinfo list if so. */ if  consider_new_or_clause(root, rel, orclause, rinfo); } } } }

上面作者详细介绍成为框架结构师须要求上学的知识点:

慎始而敬终连接

所谓原原本本连接,正是重用 TCP连接,三个HTTP央浼公用二个TCP连接。

HTTP 1.1 改换了 HTTP 左券的语义,私下认可使用持久连接。换句话说,除非显明报告(通过 Connection: close 首部),不然服务器默许会保持TCP连接张开。假设你使用的是 HTTP 1.1,从技艺上说不必要 Connection: Keep-Alive 首部,但不菲顾客端只怕选择丰裕它,比如大家的浏览器在提倡呼吁的时候,日常会暗中认可帮我们带上 Connection: Keep-Alive 首部。

咱俩来看一下为什么漫长连接对我们的话那样重大。

若是叁个网页仅富含二个HTML文书档案及三个CSS样式文件,服务器响应那多个公文的年华独家为40ms及20ms,服务器和浏览者分别在福冈和温哥华,两个之间单向光导纤维延迟为28ms(假如的能够状态,实际会比这些要大)。

  1. 率先是猎取HTML文书档案的央浼进度:

bwin手机版客户端 1img

HTML下载完结后,TCP连接关闭。

  1. 说不上,发起CSS财富的乞请,再度经历壹回TCP握手

bwin手机版客户端 2img

能够看来,七个HTTP须求都各自供给经验三回TCP的一遍握手时间,其他,图中绝非反映到的是,每三回TCP乞求都有相当的大或者会经历叁遍TCP慢运营进度,那是熏陶扩散性能的贰个不行忽略的基本点因素。

设若大家底层的TCP连接得到重用,那时候的情状会是那样子:

bwin手机版客户端 3img

很显眼,在猎取CSS的伸手中,减弱了贰遍握手往返。

一初叶,每种央求要用七个TCP连接,总延迟为284ms。在使用长久连接后,幸免了二遍握手往返,总延迟减少为228ms。那其间五遍呼吁节省了56ms(一个RTT,Round-Trip Time)的时间

地方的例子还只是唯有三个HTML和四个CSS的大致假诺情况,而实际世界的web的HTTP诉求数量比这些要多得多,在启用长久连接的图景下,N次哀告节省的总延迟时间便是×RTT。

现真实情形况中,延迟更加高、必要越多,品质提高效果比这里还要高得多。事实上,网络延迟越高,央求越来越多,节省的大运就越来越多。实际利用中,这一个节省的总时间可按秒来算了。假若每多个HTTP都重启一个TCP连接,由此可见要浪费多少时间!

三、参考资料

planmain.c

一、布满式框架结构

public class SingletonDemo1 { private static SingletonDemo1 instance; private SingletonDemo1(){} public static SingletonDemo1 getInstance(){ if (instance == null) { instance = new SingletonDemo1(); } return instance; }}

HTTP管道

从始至终 HTTP 能够让我们选拔已部分接二连三来成功多次施用央浼,但屡屡伸手必须从严满意先进先出(FIFO,first in first out)的行列顺序:发送恳求,等待响应达成,再发送顾客端队列中的下一个伸手。

举一下上一节持久连接的十三分例子,首先,服务器管理完第一回呼吁后,会时有产生了二回完整的往返:先是响应回传,接着是第二回呼吁,在第壹遍呼吁到达服务器之间的这段时光里,服务器空闲。

一旦服务器能在管理完第一遍呼吁后,立刻初叶拍卖第一回呼吁呢?以至,假如服务器能够并行管理多少个诉求呢?

此刻候HTTP管道就派上用场了,HTTP管道是多个相当小但对上述工作流特别关键的贰遍优化。

有了HTTP管道,大家的HTTP诉求在一定水平上永不再三个一个地串行诉求,而是可以八个相互了,看起来好像特别不错:

bwin手机版客户端 4img

如上海教室,HTML和CSS的伸手同临时间达到服务器,服务器同一时间管理,然后回来。

那二回,通过采取HTTP管道,又回退了两回呼吁之间的贰遍来回,总延迟减弱为 172 ms。从一开首并未有悠久连接、未有管道的284ms,到优化后的172ms,那四分之一的品质升高完全拜轻易的公约优化所赐。

等一下,刚刚这个例子好像何地还非常不够好:既然央浼同期达到,同一时候管理,为何后边要先回到HTML,然后再回到CSS?两个不可能何况重回吗?

好好很富饶,现实却某些骨感,那就是HTTP 1.1管道的贰个不小的局限性:HTTP央求不能够很好地使用多路复用,不容许一个接连上的多少个响应数据交错重临。由此一个响应必得完全再次来到后,下贰个响应才会开首传输。

那些管道只是让大家把FIFO队列从顾客端迁移到了服务器。也正是说,央求可以而且达到服务器,服务器也足以同一时间管理八个公文,可是,八个文件只怕得按顺序再次来到给客户,如下图:

bwin手机版客户端 5img

  • HTML和CSS央求同不常间达到,但先处理的是HTML央求
  • 服务器并行管理八个需要,在这之中拍卖 HTML 用时40ms,处理CSS用时20ms
  • CSS须要先拍卖完结,但被缓冲起来以等候HTML响应头阵送
  • 发送完HTML响应后,再发送服务器缓冲中的CSS响应

能够看到,尽管客商端同时发送了八个乞求,何况CSS能源先策动妥善,可是服务器也会首发送 HTML 响应,然后再付出 CSS。

题外话 下边两节举的例子,提及了HTML和CSS央浼同不时间到达,那是书中的例子,实际上,个人认为那么些例子举得不是很体面。 实际的web中,HTML及其富含的CSS平时不会同时达到服务器,正常的瀑布图亦非如此的,往往是要先获得HTML内容后浏览器技艺倡导当中的CSS等能源诉求。小编想小编只是为着解说原理吧,个人认为换到同叁个HTML文书档案中CSS和JS大概一发合适。

以此主题素材的规律在于TCP层面包车型客车“队首阻塞”,感兴趣能够去复习下Computer网络的科目。其代价往往是:不能够足够利用网络连接,形成服务器缓冲费用,有希望导致顾客端更加大的推迟。更严重的时,借使前边的央浼无有效期挂起,也许要花非常长日子能力管理完,全体继续的乞求都将被卡住,等待它做到。

故此,在HTTP 1.第11中学,管道手艺的利用很简单,尽管其优点不容置疑。实际上,一些帮忙管道的浏览器,平常都将其看做三个高等配置选项,但好多浏览器都会禁止使用它。换句话说,作为前端程序猿,开荒的接纳是面向普通浏览器选拔的话,仍旧不要过多的只求HTTP管道,看来犹盼一下HTTP 2.0中对管道的优化吧。

不过,实际上照旧有很好地应用HTTP管道的某些利用,比如在WWDC 二〇一三上,有苹果的程序猿共享了三个针对HTTP优化获得巨大效应的案例:通过运用HTTP的长久连接和管道,重用iTunes中既有的TCP连接,使得低网速客户的性质进步到原本的3倍!

实在假如你想丰盛利用管道的好处,必供给力保上边这几点原则:

  • HTTP客商端帮助管道
  • HTTP服务器辅助管道
  • 利用能够拍卖搁浅的连接并上升
  • 运用能够管理中断必要的幂等难题
  • 接纳能够有限支持自个儿不受出标题标代办的熏陶

因为iTunes的服务器和顾客端都受开辟者调节的行使,所以他们能满足以上的尺度。这说不定能给开辟hybrid应用恐怕支付浏览器之外的web应用的前端程序员们有的启示,若是您付出的网址面向的顾客是选择有滋有味的浏览器,你可能就没辙了。

布满式架构是 遍布式计算手艺的接纳和工具,近日成熟的手艺包含J2EE, CORBA和.NET,这个技艺牵扯的剧情特别广:

这种写法lazy loading很扎眼,然则致命的是在多线程不能够寻常干活。

使用七个TCP连接

因为HTTP 1.1管道存在上面包车型客车劣点,所以利用率不高。那么难点来了:假诺没有选取HTTP管道,我们的具备HTTP乞请都只可以通过悠久连接,叁个接贰个地串行再次来到,那得有多慢?

骨子里,现阶段的浏览器商家采取了别的的主意来化解HTTP 1.1管道的欠缺:允许咱们相互张开多个TCP会话。至于是有个别个,我们可能早就似曾相识:4到8个不等。那正是前面贰个程序员极其熟习的浏览器只允许从同一个服务器并行加载4到8个资源这一认知的确实来历。

HTTP长久连接纵然帮大家缓和了TCP连接复用的标题,但是当前的HTTP管道却力不从心落到实处多少个诉求结果的交错再次来到,所以浏览器只可以展开多个TCP连接,以完结并行地加载能源的指标。

只可以说,那是用作绕过使用左券限制的一个权宜之计。能够这样打多少个比喻,三个水管不能同有的时候候运输种种液体,那就不得不给各样液体开通一条运输管了,至于这么些水管哪一天能够智能化到况且运输分歧的液体,又能确定保障各自完整不受忧愁达到目标地并在目标地自行分类?照旧那一句,期望HTTP 2.0啊。

这里的连接数为何是4到8个,是多方面平衡的结果:这么些数字越大,顾客端和服务器的能源占用更加的多(在高并发访谈的服务器中因为TCP连接产生的种类开荒不可忽略),每一个主机4到8个接二连三只不过是我们都觉着比较安全的三个数字。

bwin手机版客户端 6

public class SingletonDemo2 { private static SingletonDemo2 instance; private SingletonDemo2(){} public static synchronized SingletonDemo2 getInstance(){ if (instance == null) { instance = new SingletonDemo2(); } return instance; }}

域名分区

前方提及,浏览器和服务器之间只能并发4到8个TCP连接,也正是同期下载4到8个能源,够啊?

看看大家前天的绝大相当多网址,动不动就几12个JS、CSS,一回八个,会招致前边大批量的能源排队等待;别的,只下载6个能源,对带宽的利用率也是好低的。

打个比方,二个厂子装了100根水管,每一次却不得不用在那之中6根接水,既慢,又浪费水管!

据此,大家前端质量优化中有二个最棒实行:使用域名分区

对啊,何须把自个儿只限制在二个主机上啊?大家得以手工业将富有资源分散到八个子域名,由于主机名称不相同等了,就足以突破浏览器的总是限制,达成越来越高的并行技艺。

透过这种方法“欺诈”浏览器,那样浏览器和服务器之间的并行传输数量就变多了。

域名分区使用得更加多,并行本领就越强!

不过,域名分区也有代价的!

实践中,域名分区日常会被滥用。

例如,要是你的选用面向的是2G网络的手提式无线电话机顾客,你分配了一些个域名,同期加载十几26个CSS、JS,这里的标题在于:

  • 每三个域名都会多出来的DNS查询支付,这是相当的机械财富开荒和额外的互连网延时代价。2G网络的DNS查询可不像您公司的微管理器同样,相反大概是少数秒的延期
  • 还要加载四个能源,以2G网络那种小得要命的带宽来看,后果往往正是带宽被占满,每一种财富都下载得异常慢
  • 手提式有线电话机的功耗加速

故此在有个别低带宽高延时的情景,譬如2G有线电话互联网,域名分区做过了的话,不光不会带来前端质量的升高,反而会产生性能剑客。

域名分区是一种客观但又不圆满的优化花招,最合适的法子便是,从细微分区数目开头,然后每个扩大分区并衡量分区后对选取的影响,进而赢得八个最优的域名数。

二、工程化

这种写法在getInstance()方法中投入了synchronized锁。能够在八线程中很好的职业,何况看起来它也装有很好的lazy loading,然而效用比比较低,并且大好些个场合下不须要一块。

老是与拼合

大家前端品质优化中有如此一个所谓的极品实行规范:合併打包JS、CSS文件,以及做CSS sprite。

今昔大家应有驾驭怎么要那样做了,实际上正是因为以往HTTP 1.1的管道太弱了,那三种技巧的效果就接近是隐式地启用了HTTP 管道:来自八个响应的数据前后相继地接二连三在一起,解决了额外的网络延迟。

实则,正是把管道进步了一层,置入了选取中,恐怕到了HTTP 2.0时代,前端技术员就无须干那样的活了吗?(HTTP 2.0的剧情下篇讲)

道理当然是那样的,连接拼合技巧一样有代价的。

  • 比如说CSS sprite,浏览器必得解析任何图片,固然实际上只展现了中间的一小块,也要一味把全副图片都保存在内部存储器中。浏览器未有艺术把不显示的一些从内部存款和储蓄器中剔除掉。
  • 再正是,既然JS、CSS合併了,带来的貌似就是容积的叠合,在带宽有限的条件下下载时间就变长,平时变成的便是页面渲染时间延后等结果。因为JavaScript 和CSS 管理器都不容许递增式实践的,对于JavaScript 和CSS 的分析及推行,则要等到方方面面文件下载达成。

装进文件到底多大方便呢?缺憾的是,没有出彩的分寸。然则,GooglePageSpeed团队的测量检验证明,30~50 KB是每一个JavaScript 文件大小的得当范围:既大到了能够收降低文件带来的互联网延迟,还可以有限支撑递增及分层式的实行。具体的结果恐怕会出于应用项目和本子数量而有所分裂。

1、Maven

public class SingletonDemo3 { private static SingletonDemo3 instance = new SingletonDemo3(); private SingletonDemo3(){} public static SingletonDemo3 getInstance(){ return instance; }}

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