PostgreSQL——查询重写——删除重写规则以及对查询树进行重写
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2021SC@SDUSC
目录
概述
我负责的PostgreSQL代码部分:查询的编译与执行
此篇博客的分析内容:查询重写的处理操作——删除重写规则和查询树的重写
在上篇博客中,我详细的介绍了查询重写的处理操作中的一部分——定义规则。既然知道了如何定义规则之后,那如果规则不需要了或者错误了,就需要了解如何删除重写规则。所以我再详细的介绍一下删除重写规则
查询重写——删除重写规则
经过网上查询相关资料发现,在原来的PostgreSQL版本里删除重写规则有两种方式可选分别是:根据规则的名字删除和根据规则的oid删除。使用drop rule命令删除规则时,默认是根据规则名删除的。但是,在PostgreSQL12.0版本中,搜索不到根据规则名称删除的函数——RemoveRewriteRule而只有根据规则oid删除的函数——RemoveRewriteRuleByld。我个人猜测,可能根据名字删除会不会导致重名规则等其他规则被删除,这样可能没有根据唯一标识规则的oid删除更准确。(纯属个人推测,不认同的朋友或者有其他想法的朋友,欢迎留言交流)
删除重写规则的主要函数——RemoveRewriteRuleById函数
void
RemoveRewriteRuleById(Oid ruleOid)
{
Relation RewriteRelation;
ScanKeyData skey[1];
SysScanDesc rcscan;
Relation event_relation;
HeapTuple tuple;
Oid eventRelationOid;
//打开系统表pg_rewrite,并对pg_rewrite系统表加RowExclusiveLock锁,从而防止在该表上执行insert,update,delete操作
RewriteRelation = table_open(RewriteRelationId, RowExclusiveLock);
//利用制定规则的oid,在系统表pg_rewrite中找到该规则所对应的元组
//初始化scankey
ScanKeyInit(&skey[0],
Anum_pg_rewrite_oid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(ruleOid));
//ObjectIdGetDatum(ruleOid)该函数根据规则oid取到数据
//扫描系统表pg_rewrite,找到给定的规则oid对应的元组
rcscan = systable_beginscan(RewriteRelation, RewriteOidIndexId, true,
NULL, 1, skey);
//根据rcscan获得元组所对应的数据
tuple = systable_getnext(rcscan);
//如果给定的规则oid在系统表中找不到则报错
if (!HeapTupleIsValid(tuple))
elog(ERROR, "could not find tuple for rule %u", ruleOid);
//根据元组中的ev_class字段获取该规则所作用的关联表,并对该表添加AccessExclusiveLock锁,防止对它进行修改和删除等操作
eventRelationOid = ((Form_pg_rewrite) GETSTRUCT(tuple))->ev_class;//根据元组中的ev_class字段获取该规则所作用的关联表的oid
event_relation = table_open(eventRelationOid, AccessExclusiveLock);//对表添加AccessExclusiveLock锁,防止对它进行修改和删除等操作
//删除系统表pg_rewrite中该规则所对应的元组,并关闭该系统表
CatalogTupleDelete(RewriteRelation, &tuple->t_self);
//结束刚才的扫描
systable_endscan(rcscan);
//关闭系统表pg_rewrite,并释放锁
table_close(RewriteRelation, RowExclusiveLock);
//更新该规则所作用的表的RelationData结构
CacheInvalidateRelcache(event_relation);
//关闭关联表,并释放锁
table_close(event_relation, NoLock);
}
查询重写—— 对查询树进行重写
PostgreSQL会调用函数QueryRewrite来完成查询树的重写。
QueryRewrite函数
QueryRewrite(Query *parsetree)
{
uint64 input_query_id = parsetree->queryId;//查询id
List *querylist;//查询树链表
List *results;//结果集
ListCell *l;//链表节点
CmdType origCmdType;//原始命令类型
bool foundOriginalQuery;//是否找到原始查询树
Query *lastInstead;//重写的查询树
//判断是否为原始的查询树
Assert(parsetree->querySource == QSRC_ORIGINAL);
//canSetTag:查询重写时用到,如果该Query是由原始查询转换而来则此字段为假,如果Query是由查询重写或查询规划时新增加的则此字段为真
Assert(parsetree->canSetTag);
//调用RewriteQuery函数,利用非select规则,将一个查询重写为0个或多个查询
querylist = RewriteQuery(parsetree, NIL);
//通过调用函数fireRIRrules,对上一步得到的每个查询分别用RIR规则(无条件instead规则,并且只能有一个select规则动作)重写
//result置空
results = NIL;
foreach(l, querylist)
{
Query *query = (Query *) lfirst(l);
//上一步得到的每个查询分别用RIR规则(无条件instead规则,并且只能有一个select规则动作)重写
query = fireRIRrules(query, NIL);
//把重写结果加入到results结果集中
results = lappend(results, query);
}
QueryRewrite函数,将fireRIRrules函数返回的查询树组织成一个链表,对他们的canSetTag字段进行设置之后,返回给pg_rewrite_query。到这里整个查询重写工作,就结束了。最终生成的是一个有多棵查询树组成的查询树链表,该链表将会传递给查询规划模块,形成执行计划。
//将查询树作为查询重写的结果返回
origCmdType = parsetree->commandType;//将原始查询树的命令类型记录下来
foundOriginalQuery = false;//foundOriginalQuery变量记录是否找到原始查询树
lastInstead = NULL;
foreach(l, results)//遍历查询树
{
Query *query = (Query *) lfirst(l);//取左子树
//判断结果集中是否为原始的查询树,即未被fireRIRrules函数重写
if (query->querySource == QSRC_ORIGINAL)//如果找到原始查询树
{
Assert(query->canSetTag);
Assert(!foundOriginalQuery);
foundOriginalQuery = true;//找到原始查询树则将foundOriginalQuery 变量设为true
#ifndef USE_ASSERT_CHECKING
break;
#endif
}
else//如果没找到原始查询树即已经被fireRIRrules函数重写
{
Assert(!query->canSetTag);
//判断是否符合重写后的条件
if (query->commandType == origCmdType &&
(query->querySource == QSRC_INSTEAD_RULE ||
query->querySource == QSRC_QUAL_INSTEAD_RULE))
lastInstead = query;
}
}
//如果已经进行重写并且符合条件的则将canSetTag设置为true进行标记
if (!foundOriginalQuery && lastInstead != NULL)
//canSetTag:查询重写时用到,如果该Query是由原始查询转换而来则此字段为假,如果Query是由查询重写或查询规划时新增加的则此字段为真
lastInstead->canSetTag = true;
//返回查询树
return results;
}
QueryRewrite函数调用的RewriteQuery函数——处理非select规则的重写
RewriteQuery函数的作用是执行非SELECT规则(也就是处理SELECT以外的语句)
static List *
RewriteQuery(Query *parsetree, List *rewrite_events)
{
CmdType event = parsetree->commandType;
bool instead = false;
bool returning = false;
bool updatableview = false;
Query *qual_product = NULL;
List *rewritten = NIL;
ListCell *lc1;
//首先寻找含有INSERT/UPDATE/DELETE的WITH子句(说白了就是CTE)。如果存在,那么就调用自身递归地重写它们;
//扫描查询树链表,处理WITH子句中的所有CTE
foreach(lc1, parsetree->cteList)
{
CommonTableExpr *cte = lfirst_node(CommonTableExpr, lc1);
Query *ctequery = castNode(Query, cte->ctequery);
List *newstuff;
//如果cte的命令类型为select则跳过不进行处理
if (ctequery->commandType == CMD_SELECT)
continue;
//递归重写update,delete,insert三种类型的with子句
newstuff = RewriteQuery(ctequery, rewrite_events);
//用重写后的query覆盖CTE中的查询,对CTE,只支持单条语句的DO INSTEAD规则,其他情况都报错
//判断是否只有一个instead规则
if (list_length(newstuff) == 1)
{
//把单个查询树写回cte节点
ctequery = linitial_node(Query, newstuff);
cte->ctequery = (Node *) ctequery;
}
//如果没有instead规则则报错
else if (newstuff == NIL)
{
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("DO INSTEAD NOTHING rules are not supported for data-modifying statements in WITH")));
}
//只支持单条语句的DO INSTEAD规则,其他情况都报错
else
{
ListCell *lc2;
//遍历查询树,决定判断报出什么样的错误信息提示
foreach(lc2, newstuff)
{
Query *q = (Query *) lfirst(lc2);
//只支持单条语句的DO INSTEAD规则,其他情况都报错
if (q->querySource == QSRC_QUAL_INSTEAD_RULE)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("conditional DO INSTEAD rules are not supported for data-modifying statements in WITH")));
if (q->querySource == QSRC_NON_INSTEAD_RULE)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("DO ALSO rules are not supported for data-modifying statements in WITH")));
}
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("multi-statement DO INSTEAD rules are not supported for data-modifying statements in WITH")));
}
}
//判断如果查询语句不是SELECT和UTILITY
if (event != CMD_SELECT && event != CMD_UTILITY)
{
int result_relation;
RangeTblEntry *rt_entry;
Relation rt_entry_relation;
List *locks;
List *product_queries;
bool hasUpdate = false;
int values_rte_index = 0;
bool defaults_remaining = false;
//根据result_relation在范围表rtable中,找到对应的项rt_entry
result_relation = parsetree->resultRelation;
//result_relation范围表不能为空
Assert(result_relation != 0);
//在范围表rtable中取得rt_entry项
rt_entry = rt_fetch(result_relation, parsetree->rtable);
Assert(rt_entry->rtekind == RTE_RELATION);
//打开rte对应的表
rt_entry_relation = table_open(rt_entry->relid, NoLock);
//对不同语句类型做分别处理:重写targetList
//如果是insert规则类型
if (event == CMD_INSERT)
{
RangeTblEntry *values_rte = NULL;
//判断是否为单个rte
if (list_length(parsetree->jointree->fromlist) == 1)
{ //初始化目标链表
RangeTblRef *rtr = (RangeTblRef *) linitial(parsetree->jointree->fromlist);
//判断初始化是否成功
if (IsA(rtr, RangeTblRef))
{
RangeTblEntry *rte = rt_fetch(rtr->rtindex,
parsetree->rtable);
//如果有VALUES,则获得其对应的RTE
if (rte->rtekind == RTE_VALUES)
{
values_rte = rte;
values_rte_index = rtr->rtindex;
}
}
}
//如果上一步获得了对应的rte
if (values_rte)
{
//重写INSERT的targetList
parsetree->targetList = rewriteTargetListIU(parsetree->targetList,
parsetree->commandType,
parsetree->override,
rt_entry_relation,
parsetree->resultRelation);
//重写VALUES,把DEFAULT变成缺省值表达式
if (!rewriteValuesRTE(parsetree, values_rte, values_rte_index,
rt_entry_relation, false))
defaults_remaining = true;
}
else//如果没有获得对应的rte
{
//重写INSERT的targetList(无values情况)
parsetree->targetList =
rewriteTargetListIU(parsetree->targetList,
parsetree->commandType,
parsetree->override,
rt_entry_relation,
parsetree->resultRelation);
}
}
//如果是update规则类型
else if (event == CMD_UPDATE)
{ 重写update的targetList
parsetree->targetList =
rewriteTargetListIU(parsetree->targetList,
parsetree->commandType,
parsetree->override,
rt_entry_relation,
parsetree->resultRelation);
}
//如果是delete规则类型,则不进行任何操作
else if (event == CMD_DELETE)
{
}
else//如果是insert,update,delete类型之外的其他类型则报错
elog(ERROR, "unrecognized commandType: %d", (int) event);
//获得匹配的规则,规则保存在RelationData结构中的rd_rules,其类型是RuleLock(rewrite/prs2lock.h))
locks = matchLocks(event, rt_entry_relation->rd_rules,
result_relation, parsetree, &hasUpdate);
//用于对上面判断出来合适的规则进行循环处理
product_queries = fireRules(parsetree,
result_relation,
event,
locks,
&instead,
&returning,
&qual_product);
}
//如果没有INSTEAD规则,并且是个视图,该视图没有INSTEAD触发器) (该视图必须是可更新视图)
if (!instead && qual_product == NULL &&
rt_entry_relation->rd_rel->relkind == RELKIND_VIEW &&
!view_has_instead_trigger(rt_entry_relation, event))
{
//rewriteTargetView函数内部判断是否为可更新视图,如果不是可更新视图则报错
parsetree = rewriteTargetView(parsetree, rt_entry_relation);
//判断,如果是insert规则类型
if (parsetree->commandType == CMD_INSERT)
//把原来的query加到product_queries,加在前面或者后面
//加到product_queries开头
product_queries = lcons(parsetree, product_queries);
else//加到product_queries结尾
product_queries = lappend(product_queries, parsetree);
//把instead和returning设为true,防止原始查询再次被包含在下面
instead = true;
returning = true;
updatableview = true;
}
//product_queries是在fireRules函数中生成的所有规则的动作语句
//判断product_queries是否为空
if (product_queries != NIL)
{
ListCell *n;
rewrite_event *rev;
//遍历rewrite_events
foreach(n, rewrite_events)
{
rev = (rewrite_event *) lfirst(n);
//检查规则是否是递归,如果是无穷递归则报错
if (rev->relation == RelationGetRelid(rt_entry_relation) &&
rev->event == event)
ereport(ERROR,
(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
errmsg("infinite recursion detected in rules for relation \\"%s\\"",
RelationGetRelationName(rt_entry_relation))));
}
//创建rewritten_event,并添加到列表rewritten_events的开头
rev = (rewrite_event *) palloc(sizeof(rewrite_event));//分配内存
rev->relation = RelationGetRelid(rt_entry_relation);//获取oid
rev->event = event;//获取event
rewrite_events = lcons(rev, rewrite_events);//添加到链表开头
//重写规则中的动作语句
foreach(n, product_queries)
{
Query *pt = (Query *) lfirst(n);
List *newstuff;
//调用RewriteQuery函数递归重写规则中的动作语句
newstuff = RewriteQuery(pt, rewrite_events);
//把重写结果加到rewritten列表中
rewritten = list_concat(rewritten, newstuff);
}
//从rewritten_events的开头删除rewritten_event
rewrite_events = list_delete_first(rewrite_events);
}
//如果有INSTEAD规则并且原始查询有RETURNING子句,而规则动作中没有RETURNING,则报错
if ((instead || qual_product != NULL) &&
parsetree->returningList &&
!returning)
{
switch (event)
{
case CMD_INSERT:
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot perform INSERT RETURNING on relation \\"%s\\"",
RelationGetRelationName(rt_entry_relation)),
errhint("You need an unconditional ON INSERT DO INSTEAD rule with a RETURNING clause.")));
break;
case CMD_UPDATE:
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot perform UPDATE RETURNING on relation \\"%s\\"",
RelationGetRelationName(rt_entry_relation)),
errhint("You need an unconditional ON UPDATE DO INSTEAD rule with a RETURNING clause.")));
break;
case CMD_DELETE:
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot perform DELETE RETURNING on relation \\"%s\\"",
RelationGetRelationName(rt_entry_relation)),
errhint("You need an unconditional ON DELETE DO INSTEAD rule with a RETURNING clause.")));
break;
default:
elog(ERROR, "unrecognized commandType: %d",
(int) event);
break;
}
}
//如果没有unqualified INSTEAD规则
if (!instead)
{ //判断是否为insert类型
if (parsetree->commandType == CMD_INSERT)
{
if (qual_product != NULL)
//把quad_product或者原来的query添加到rewritten列表的开头
rewritten = lcons(qual_product, rewritten);
else
//把quad_product或者原来的query添加到rewritten列表的结尾
rewritten = lcons(parsetree, rewritten);
}
else
{
if (qual_product != NULL)
//把quad_product或者原来的query添加到rewritten列表
rewritten = lappend(rewritten, qual_product);
else//把parsetree添加到rewritten列表
rewritten = lappend(rewritten, parsetree);
}
}
//如果重写结果包括多个非utility语句,并且原来的query中有CTE则报错
//判断原来的query中有无cte
if (parsetree->cteList != NIL)
{
int qcount = 0;
foreach(lc1, rewritten)
{
Query *q = (Query *) lfirst(lc1);
//判断是否包含多个非utility语句
if (q->commandType != CMD_UTILITY)
qcount++;
}
if (qcount > 1)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("WITH cannot be used in a query that is rewritten by rules into multiple queries")));
}
//返回写过的rewritten列表
return rewritten;
}
QueryRewrite函数调用的fireRIRrules函数——处理select规则的重写
fireRIRrules函数在每一个RTE上应用所有的RIR规则
static Query *
fireRIRrules(Query *parsetree, List *activeRIRs)
{
int origResultRelation = parsetree->resultRelation;//结果表
int rt_index;//RTE的index
ListCell *lc;//临时变量
//遍历该查询树的每一个范围表
rt_index = 以上是关于PostgreSQL——查询重写——删除重写规则以及对查询树进行重写的主要内容,如果未能解决你的问题,请参考以下文章
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