PostgreSQL 执行Drop Table等命令型SQL的总体流程

概述DROP命令（Commands）实现： /* * Drop one or more objects. * * We don't currently handle all object types here. Relations, for example, * require special handling, because (for example) indexes have addi

DROP命令（Commands）实现：

/* * Drop one or more objects. * * We don't currently handle all object types here.  Relations,for example,* require special handling,because (for example) indexes have additional * locking requirements. * * We look up all the objects first,and then delete them in a single * performMultipleDeletions() call.  This avoIDs unnecessary DROP RESTRICT * errors if there are dependencIEs between them. */voIDRemoveObjects(DropStmt *stmt)/* * dispatch function for DropStmt */static voIDExecDropStmt(DropStmt *stmt,bool istopLevel){	switch (stmt->removeType)	{		case OBJECT_INDEX:			if (stmt->concurrent)				PreventTransactionChain(istopLevel,"DROP INDEX CONCURRENTLY");			/* fall through */		case OBJECT_table:		case OBJECT_SEQUENCE:		case OBJECT_VIEW:		case OBJECT_MATVIEW:		case OBJECT_FOREIGN_table:			RemoveRelations(stmt);			break;		default:			RemoveObjects(stmt);			break;	}}/* * standard_ProcessUtility itself deals only with utility commands for * which we do not provIDe event trigger support.  Commands that do have * such support are passed down to ProcessUtilitySlow,which contains the * necessary infrastructure for such triggers. * * This division is not just for performance: it's critical that the * event trigger code not be invoked when doing START TRANSACTION for * example,because we might need to refresh the event trigger cache,* which requires being in a valID transaction. */voIDstandard_ProcessUtility(Node *parsetree,const char *queryString,ProcessUtilityContext context,ParamListInfo params,DestReceiver *dest,char *completionTag)/* * ProcessUtility *		general utility function invoker * *	parsetree: the parse tree for the utility statement *	queryString: original source text of command *	context: IDentifIEs source of statement (toplevel clIEnt command,*		non-toplevel clIEnt command,subcommand of a larger utility command) *	params: parameters to use during execution *	dest: where to send results *	completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE *		in which to store a command completion status string. * * Notes: as of PG 8.4,caller MUST supply a queryString; it is not * allowed anymore to pass NulL.  (If you really don't have source text,* you can pass a constant string,perhaps "(query not available)".) * * completionTag is only set nonempty if we want to return a nondefault status. * * completionTag may be NulL if caller doesn't want a status string. */voIDProcessUtility(Node *parsetree,char *completionTag)

详细调用栈如下：

#0  ExecDropStmt (stmt=0x17e9b40,istopLevel=1 '1') at utility.c:1349#1  0x0000000000759457 in ProcessUtilitySlow (parsetree=0x17e9b40,queryString=0x17e90b0 "drop table t1;",context=PROCESS_UTIliTY_topLEVEL,params=0x0,dest=0x17e9ea0,completionTag=0x7fff06aee670 "") at utility.c:1296#2  0x0000000000758849 in standard_ProcessUtility (parsetree=0x17e9b40,completionTag=0x7fff06aee670 "") at utility.c:792#3  0x0000000000757c88 in ProcessUtility (parsetree=0x17e9b40,completionTag=0x7fff06aee670 "") at utility.c:310#4  0x0000000000756e92 in PortalRunUtility (portal=0x1822d70,utilityStmt=0x17e9b40,istopLevel=1 '1',completionTag=0x7fff06aee670 "")    at pquery.c:1187#5  0x0000000000757048 in PortalRunMulti (portal=0x1822d70,altdest=0x17e9ea0,completionTag=0x7fff06aee670 "") at pquery.c:1318#6  0x000000000075661c in PortalRun (portal=0x1822d70,count=9223372036854775807,completionTag=0x7fff06aee670 "") at pquery.c:816#7  0x0000000000750944 in exec_simple_query (query_string=0x17e90b0 "drop table t1;") at postgres.c:1045#8  0x0000000000754967 in PostgresMain (argc=1,argv=0x1784148,dbname=0x1784130 "wzy",username=0x1784110 "xiaochu.yh") at postgres.c:4004#9  0x00000000006e80ba in BackendRun (port=0x17a3e00) at postmaster.c:4117#10 0x00000000006e77fd in BackendStartup (port=0x17a3e00) at postmaster.c:3791#11 0x00000000006e41b2 in ServerLoop () at postmaster.c:1570#12 0x00000000006e392e in PostmasterMain (argc=3,argv=0x1783380) at postmaster.c:1223#13 0x000000000064d3d3 in main (argc=3,argv=0x1783380) at main.c:225

Portal，入口的意思。Postgre中，Portal是个抽象概念，它表示一个正在运行或可运行query的执行状态。

对于可以生成执行计划的SQL语句（planable sql），都通过Processquery来处理；对于不能生成执行计划的SQL语句，取名为命令型sql（Command sql），都通过PortalRunUtility来处理。

参考：

1. gdb使用http://blog.chinaunix.net/uID-20788636-ID-1841301.HTML

2. postgre编译安装启动http://blog.chinaunix.net/uID-11161675-ID-2903295.HTML

3. postgre官方文档http://www.postgresql.org/docs/current/static/index.HTML

4. 如何做postgre源码分析http://blog.csdn.net/anzelin_ruc/article/details/8622770

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