PostgreSQL数据库扩展包——原理CreateExtension扩展控制文件解析

快来打我* 2022-10-12 04:19 421阅读 0赞

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## createExtension函数 ##

首先看createExtension函数，该函数首先调用check\_valid\_extension\_name函数在任何访问文件系统之前检测extension的名字的合法性；调用get\_extension\_oid检测数据库是否已经安装该扩展（参加[PostgreSQL数据库TableAM——systable操作][PostgreSQL_TableAM_systable]）；使用全局变量creating\_extension确保同一时刻只能创建一个扩展；通过遍历CreateExtensionStmt结构体，初始化d\_schema、d\_new\_version、d\_old\_version、d\_cascade等变量；最后调用CreateExtensionInternal(stmt->extname, schemaName, versionName, oldVersionName, cascade, NIL, true)函数。

ObjectAddress CreateExtension(ParseState *pstate, CreateExtensionStmt *stmt) { 
    	DefElem    *d_schema = NULL;
    	DefElem    *d_new_version = NULL;
    	DefElem    *d_old_version = NULL;
    	DefElem    *d_cascade = NULL;
    	char	   *schemaName = NULL;
    	char	   *versionName = NULL;
    	char	   *oldVersionName = NULL;
    	bool		cascade = false;
    	ListCell   *lc;
    	check_valid_extension_name(stmt->extname);
    	if (get_extension_oid(stmt->extname, true) != InvalidOid){ 
    		if (stmt->if_not_exists){  ereport(NOTICE,(errcode(ERRCODE_DUPLICATE_OBJECT),errmsg("extension \"%s\" already exists, skipping",stmt->extname)));return InvalidObjectAddress;
    		}else
    			ereport(ERROR,(errcode(ERRCODE_DUPLICATE_OBJECT),errmsg("extension \"%s\" already exists",stmt->extname))); }
    	/* We use global variables to track the extension being created, so we can create only one extension at the same time. */
    	if (creating_extension)
    		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("nested CREATE EXTENSION is not supported")));
    	/* Deconstruct the statement option list */
    	foreach(lc, stmt->options){ 
    		DefElem    *defel = (DefElem *) lfirst(lc);
    		if (strcmp(defel->defname, "schema") == 0) { 
    			if (d_schema) ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("conflicting or redundant options"), parser_errposition(pstate, defel->location)));
    			d_schema = defel;
    			schemaName = defGetString(d_schema);
    		} else if (strcmp(defel->defname, "new_version") == 0) { 
    			if (d_new_version) ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("conflicting or redundant options"), parser_errposition(pstate, defel->location)));
    			d_new_version = defel;
    			versionName = defGetString(d_new_version);
    		} else if (strcmp(defel->defname, "old_version") == 0) { 
    			if (d_old_version) ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("conflicting or redundant options"), parser_errposition(pstate, defel->location)));
    			d_old_version = defel;
    			oldVersionName = defGetString(d_old_version);
    		} else if (strcmp(defel->defname, "cascade") == 0) { 
    			if (d_cascade)
    				ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("conflicting or redundant options"), parser_errposition(pstate, defel->location)));
    			d_cascade = defel;
    			cascade = defGetBoolean(d_cascade);
    		} else
    			elog(ERROR, "unrecognized option: %s", defel->defname);
    	}
    	/* Call CreateExtensionInternal to do the real work. */
    	return CreateExtensionInternal(stmt->extname, schemaName, versionName, oldVersionName, cascade, NIL, true);
    }

### CreateExtensionInternal函数 ###

`static ObjectAddress CreateExtensionInternal(char *extensionName, char *schemaName, const char *versionName, const char *oldVersionName, bool cascade, List *parents, bool is_create)`当指定cascade，如果依赖的扩展需要被安装，则会递归调用CreateExtensionInternal函数。parent列表参数包含已经安装的扩展。

static ObjectAddress CreateExtensionInternal(char *extensionName, char *schemaName, const char *versionName, const char *oldVersionName, bool cascade, List *parents, bool is_create) { 
    	char	   *origSchemaName = schemaName;
    	Oid			schemaOid = InvalidOid;
    	Oid			extowner = GetUserId();
    	ExtensionControlFile *pcontrol;
    	ExtensionControlFile *control;
    	List	   *updateVersions;
    	List	   *requiredExtensions;
    	List	   *requiredSchemas;
    	Oid			extensionOid;
    	ObjectAddress address;
    	ListCell   *lc;
    	/* Read the primary control file. Note we assume that it does not contain any non-ASCII data, so there is no need to worry about encoding at this point. */
    	pcontrol = read_extension_control_file(extensionName);

read\_extension\_control\_file读取primary control file，主要调用parse\_extension\_control\_file函数。parse\_extension\_control\_file函数解析控制文件，取出调用具体版本，文件名等信息。如果version为NULL，则进行primary file的处理；否则进行optional auxiliary文件的处理。get\_extension\_control\_filename(control->name)函数获取文件全路径sharepath/extension/extname.control。将文件内容读取并将键值内容转换ConfigVariable列表，并将其值赋给ExtensionControlFile结构体相应的成员。

static ExtensionControlFile *read_extension_control_file(const char *extname) { 
    	ExtensionControlFile *control;
    	/* Set up default values. Pointer fields are initially null. */
    	control = (ExtensionControlFile *) palloc0(sizeof(ExtensionControlFile));
    	control->name = pstrdup(extname);
    	control->relocatable = false;
    	control->superuser = true;
    	control->encoding = -1;
    	/* Parse the primary control file. */
    	parse_extension_control_file(control, NULL);
    	return control;
    }
    
    static void parse_extension_control_file(ExtensionControlFile *control, const char *version){ 
    	char	   *filename;
    	FILE	   *file;
    	ConfigVariable *item, *head = NULL, *tail = NULL;
    	/* Locate the file to read. Auxiliary files are optional. */
    	if (version)
    		filename = get_extension_aux_control_filename(control, version);
    	else
    		filename = get_extension_control_filename(control->name);
    	if ((file = AllocateFile(filename, "r")) == NULL) { 
    		if (version && errno == ENOENT) {  /* no auxiliary file for this version */		
    			pfree(filename); return;
    		}
    		ereport(ERROR, (errcode_for_file_access(), errmsg("could not open extension control file \"%s\": %m", filename)));
    	}
    
    	/* Parse the file content, using GUC's file parsing code. We need not check the return value since any errors will be thrown at ERROR level. */
    	(void) ParseConfigFp(file, filename, 0, ERROR, &head, &tail);
    	FreeFile(file);
    	/* Convert the ConfigVariable list into ExtensionControlFile entries. */
    	for (item = head; item != NULL; item = item->next){ 
    		if (strcmp(item->name, "directory") == 0){ 
    			if (version) ereport(ERROR,(errcode(ERRCODE_SYNTAX_ERROR), errmsg("parameter \"%s\" cannot be set in a secondary extension control file", item->name)));
    			control->directory = pstrdup(item->value);
    		} else if (strcmp(item->name, "default_version") == 0) { 
    			if (version) ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("parameter \"%s\" cannot be set in a secondary extension control file", item->name)));
    			control->default_version = pstrdup(item->value);
    		} else if (strcmp(item->name, "module_pathname") == 0) { 
    			control->module_pathname = pstrdup(item->value);
    		} else if (strcmp(item->name, "comment") == 0) { 
    			control->comment = pstrdup(item->value);
    		} else if (strcmp(item->name, "schema") == 0) { 
    			control->schema = pstrdup(item->value);
    		} else if (strcmp(item->name, "relocatable") == 0) { 
    			if (!parse_bool(item->value, &control->relocatable)) ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("parameter \"%s\" requires a Boolean value", item->name)));
    		} else if (strcmp(item->name, "superuser") == 0) { 
    			if (!parse_bool(item->value, &control->superuser)) ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("parameter \"%s\" requires a Boolean value", item->name)));
    		} else if (strcmp(item->name, "encoding") == 0) { 
    			control->encoding = pg_valid_server_encoding(item->value);
    			if (control->encoding < 0) ereport(ERROR, (errcode(ERRCODE_UNDEFINED_OBJECT), errmsg("\"%s\" is not a valid encoding name", item->value)));
    		} else if (strcmp(item->name, "requires") == 0){ 
    			/* Need a modifiable copy of string */
    			char	   *rawnames = pstrdup(item->value);
    			/* Parse string into list of identifiers */
    			if (!SplitIdentifierString(rawnames, ',', &control->requires)) { 
    				/* syntax error in name list */
    				ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("parameter \"%s\" must be a list of extension names", item->name)));
    			}
    		} else
    			ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("unrecognized parameter \"%s\" in file \"%s\"", item->name, filename)));
    	}
    	FreeConfigVariables(head);
    	if (control->relocatable && control->schema != NULL)
    		ereport(ERROR, (errcode(ERRCODE_SYNTAX_ERROR), errmsg("parameter \"schema\" cannot be specified when \"relocatable\" is true")));
    	pfree(filename);
    }

CreateExtensionInternal函数如果没有获得versionName，则需要取pcontrol->default\_version作为versionName。

/* Determine the version to install */
    	if (versionName == NULL){ 
    		if (pcontrol->default_version)
    			versionName = pcontrol->default_version;
    		else
    			ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg("version to install must be specified")));
    	}
    	check_valid_version_name(versionName);

CreateExtensionInternal函数下面的逻辑是寻找指定版本扩展的脚本，如果没有该版本的脚本，则寻找更新版本的脚本（identify\_update\_path）。

if (oldVersionName) { 
    		/* "FROM old_version" was specified, indicating that we're trying to update from some unpackaged version of the extension. Locate a series of update scripts that will do it. */
    		check_valid_version_name(oldVersionName);
    		if (strcmp(oldVersionName, versionName) == 0)
    			ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("FROM version must be different from installation target version \"%s\"",versionName)));
    		updateVersions = identify_update_path(pcontrol, oldVersionName, versionName);
    		if (list_length(updateVersions) == 1) { 
    			/* Simple case where there's just one update script to run. We will not need any follow-on update steps. */
    			Assert(strcmp((char *) linitial(updateVersions), versionName) == 0);
    			updateVersions = NIL;
    		}else{ 
    			/* Multi-step sequence. We treat this as installing the version that is the target of the first script, followed by successive updates to the later versions. */
    			versionName = (char *) linitial(updateVersions);
    			updateVersions = list_delete_first(updateVersions);
    		}
    	}else{ 
    		/* No FROM, so we're installing from scratch. If there is an install script for the desired version, we only need to run that one. */
    		char	   *filename;
    		struct stat fst;
    		oldVersionName = NULL;
    		filename = get_extension_script_filename(pcontrol, NULL, versionName);
    		if (stat(filename, &fst) == 0) { 
    			/* Easy, no extra scripts */
    			updateVersions = NIL;
    		} else { 
    			/* Look for best way to install this version */
    			List	   *evi_list;
    			ExtensionVersionInfo *evi_start;
    			ExtensionVersionInfo *evi_target;
    			/* Extract the version update graph from the script directory */
    			evi_list = get_ext_ver_list(pcontrol);
    			/* Identify the target version */
    			evi_target = get_ext_ver_info(versionName, &evi_list);
    			/* Identify best path to reach target */
    			evi_start = find_install_path(evi_list, evi_target, &updateVersions);
    			/* Fail if no path ... */
    			if (evi_start == NULL) ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("extension \"%s\" has no installation script nor update path for version \"%s\"",pcontrol->name, versionName)));
    			/* Otherwise, install best starting point and then upgrade */
    			versionName = evi_start->name;
    		}
    	}

[get\_extension\_script\_filename][get_extension_script_filename]函数调用如下：  
get\_ext\_ver\_list()：遍历所有.sql文件获取所有版本节点。  
find\_install\_path()：根据目标节点选择最短路径以及相对应的起始节点。  
find\_update\_path()：最短路径算法Dijkstra的实现。  
get\_extension\_script\_filename获取sql文件名，规则如下：  
版本命名的规则:扩展名 +“–”+“版本号”+ .sql (eg:cube–1.2.sql)  
版本与版本之间的升级采用“–”连接。(eg:cube–1.2–1.3.sql)  
Target 版本由控制文件中的default\_version确定。  
根据目标版本选择最短路径。

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为需要按照的目标版本获取control参数，read\_extension\_aux\_control\_file获取aux控制文件ExtensionControlFile结构体。

/* Fetch control parameters for installation target version */
    	control = read_extension_aux_control_file(pcontrol, versionName);

先通过schemaName获取schemaOid，如果control->schema不为NULL，使用control->schema作为schemaName，再通过该schemaName获取schemaOid，如果不存在相关schemaOid，则通过CreateSchemaCommand创建Schema。  
如果control->schema为NULL，判别先通过schemaName获取的schemaOid是否为合法，不合法则从默认creation namespace获取该schemaOid所代表的scchemaName。

/* Determine the target schema to install the extension into */
    	if (schemaName){  /* If the user is giving us the schema name, it must exist already. */
    		schemaOid = get_namespace_oid(schemaName, false); }
    	if (control->schema != NULL) { 
    		/* The extension is not relocatable and the author gave us a schema for it. Unless CASCADE parameter was given, it's an error to give a schema different from control->schema if control->schema is specified. */
    		if (schemaName && strcmp(control->schema, schemaName) != 0 && !cascade)
    			ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("extension \"%s\" must be installed in schema \"%s\"", control->name, control->schema)));
    		/* Always use the schema from control file for current extension. */
    		schemaName = control->schema;
    		/* Find or create the schema in case it does not exist. */
    		schemaOid = get_namespace_oid(schemaName, true);
    		if (!OidIsValid(schemaOid)){ 
    			CreateSchemaStmt *csstmt = makeNode(CreateSchemaStmt);
    			csstmt->schemaname = schemaName;
    			csstmt->authrole = NULL;	/* will be created by current user */
    			csstmt->schemaElts = NIL;
    			csstmt->if_not_exists = false;
    			CreateSchemaCommand(csstmt, "(generated CREATE SCHEMA command)", -1, -1);
    			/* CreateSchemaCommand includes CommandCounterIncrement, so new schema is now visible. */
    			schemaOid = get_namespace_oid(schemaName, false);
    		}
    	} else if (!OidIsValid(schemaOid)) { 
    		/* Neither user nor author of the extension specified schema; use the current default creation namespace, which is the first explicit entry in the search_path. */
    		List	   *search_path = fetch_search_path(false);
    		if (search_path == NIL) /* nothing valid in search_path? */
    			ereport(ERROR, (errcode(ERRCODE_UNDEFINED_SCHEMA), errmsg("no schema has been selected to create in")));
    		schemaOid = linitial_oid(search_path);
    		schemaName = get_namespace_name(schemaOid);
    		if (schemaName == NULL) /* recently-deleted namespace? */
    			ereport(ERROR, (errcode(ERRCODE_UNDEFINED_SCHEMA), errmsg("no schema has been selected to create in")));
    		list_free(search_path);
    	}

/* Make note if a temporary namespace has been accessed in this transaction. */
    	if (isTempNamespace(schemaOid))
    		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
    	/* * We don't check creation rights on the target namespace here. If the * extension script actually creates any objects there, it will fail if * the user doesn't have such permissions. But there are cases such as * procedural languages where it's convenient to set schema = pg_catalog * yet we don't want to restrict the command to users with ACL_CREATE for * pg_catalog. */

**查找该扩展依赖的其他扩展，并安装它们**，并将get\_required\_extension和get\_extension\_schema函数放入get\_extension\_schema和requiredSchemas列表。

/* Look up the prerequisite extensions, install them if necessary, and build lists of their OIDs and the OIDs of their target schemas. */
    	requiredExtensions = NIL;
    	requiredSchemas = NIL;
    	foreach(lc, control->requires){ 
    		char	   *curreq = (char *) lfirst(lc);
    		Oid			reqext;
    		Oid			reqschema;
    		reqext = get_required_extension(curreq,extensionName,origSchemaName,cascade,parents,is_create);
    		reqschema = get_extension_schema(reqext);
    		requiredExtensions = lappend_oid(requiredExtensions, reqext);
    		requiredSchemas = lappend_oid(requiredSchemas, reqschema);
    	}

InsertExtensionTuple():把控制文件的信息保存到Tuple中。

/* Insert new tuple into pg_extension, and create dependency entries. */
    	address = InsertExtensionTuple(control->name, extowner, schemaOid, control->relocatable, versionName, PointerGetDatum(NULL), PointerGetDatum(NULL), requiredExtensions);
    	extensionOid = address.objectId;
    	/* Apply any control-file comment on extension */
    	if (control->comment != NULL)
    		CreateComments(extensionOid, ExtensionRelationId, 0, control->comment);

execute\_sql\_string():解析sql文件。先调用pg\_parse\_query将sql转换成parsetree\_list。

/* Execute the installation script file */
    	execute_extension_script(extensionOid, control, oldVersionName, versionName, requiredSchemas, schemaName, schemaOid);
    
    	/* If additional update scripts have to be executed, apply the updates as though a series of ALTER EXTENSION UPDATE commands were given */
    	ApplyExtensionUpdates(extensionOid, pcontrol, versionName, updateVersions, origSchemaName, cascade, is_create);
    	return address;
    }

然后执行pg\_analyze\_and\_rewrite(),pg\_plan\_queries()，ExecutorRun()对每一个parse tree重写执行。

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[PostgreSQL_TableAM_systable]: https://feishujun.blog.csdn.net/article/details/118438600
[get_extension_script_filename]: https://feishujun.blog.csdn.net/article/details/118500826
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