PostgreSQL源码分析——CREATE DATABASE

这里我们分析一下在PostgreSQL中创建数据库的源码，在分析源码之前，最好先阅读《PostgreSQL指南内幕探索》的第一章，数据库集簇、数据库和数据表，弄清其空间布局，理解PG中，数据库、表、元组是怎么布局的。通俗一点说，创建一个数据库相当于创建一个数据目录，在这个目录下，存放该数据库中定义的表、索引等对象。在数据库中，存放数据最基础的是表，我们定义了很多表用来存储用户的数据，每个表是一个文件（大于1G的表会分割为多个文件），而表文件内部被划分为固定长度的页，在页中存放元组，这里可以仔细想一下为什么要这么设计？页的大小设置为多少合适？这里涉及到很多方面，比如磁盘，固态硬盘的物理特性，每次读写的最小单元是扇区或块，操作系统为了性能，往往不会按最小单元进行读写，会批量读取，比如8k为一个块进行读取，数据库为了性能会设有缓冲区，用来将最近使用或最常使用的数据缓存起来，这样能避免频繁进行磁盘读取，（PG中使用时钟扫描算法），如果表不划分为页的话，缓存，性能等都不是最合理的方案，实现索引怎么实现的？ 这里可以再读一下《数据库系统内幕》相关章节。

预分析

这我们再分析源码之前预先想一下CREATE DATABASE需要做什么，向pg_database系统表中插入一条数据，数据库名，数据库Oid等信息，创建一个数据库目录（内容从模板数据库copy，目录名为数据库oid）。我们分析一下源码看一下是不是这样。

-- 查看当前数据库
postgres@postgres=# \lList of databasesName    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   
-----------+----------+----------+-------------+-------------+-----------------------postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +|          |          |             |             | postgres=CTc/postgrestemplate1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +|          |          |             |             | postgres=CTc/postgres
(3 rows)-- 查询系统表
postgres@postgres=# select oid,datname,datdba,encoding from pg_database;oid  |  datname  | datdba | encoding 
-------+-----------+--------+----------14204 | postgres  |     10 |        61 | template1 |     10 |        614203 | template0 |     10 |        6
(3 rows)-- 查看数据目录，目录以数据库oid命名
[postgres@slpc base]$ ls
1  14203  14204postgres@postgres=# \d pg_database;Table "pg_catalog.pg_database"Column     |   Type    | Collation | Nullable | Default 
---------------+-----------+-----------+----------+---------oid           | oid       |           | not null | datname       | name      |           | not null | datdba        | oid       |           | not null | encoding      | integer   |           | not null | datcollate    | name      |           | not null | datctype      | name      |           | not null | datistemplate | boolean   |           | not null | datallowconn  | boolean   |           | not null | datconnlimit  | integer   |           | not null | datlastsysoid | oid       |           | not null | datfrozenxid  | xid       |           | not null | datminmxid    | xid       |           | not null | dattablespace | oid       |           | not null | datacl        | aclitem[] |           |          | 
Indexes:"pg_database_datname_index" UNIQUE, btree (datname), tablespace "pg_global""pg_database_oid_index" UNIQUE, btree (oid), tablespace "pg_global"
Tablespace: "pg_global"

CREATE DATABASE语法使用如下：

CREATE DATABASE name[ WITH ] [ OWNER [=] user_name ][ TEMPLATE [=] template ][ ENCODING [=] encoding ][ STRATEGY [=] strategy ] ][ LOCALE [=] locale ][ LC_COLLATE [=] lc_collate ][ LC_CTYPE [=] lc_ctype ][ ICU_LOCALE [=] icu_locale ][ LOCALE_PROVIDER [=] locale_provider ][ COLLATION_VERSION = collation_version ][ TABLESPACE [=] tablespace_name ][ ALLOW_CONNECTIONS [=] allowconn ][ CONNECTION LIMIT [=] connlimit ][ IS_TEMPLATE [=] istemplate ][ OID [=] oid ]

pg_database系统表参考文档：https://www.postgresql.org/docs/current/catalog-pg-database.html
语法参考文档：https://www.postgresql.org/docs/current/sql-createdatabase.html

源码分析

其语法相关可参考：

解析层

关键定义：

/* ----------------------*		Createdb Statement* ---------------------- */
typedef struct CreatedbStmt
{NodeTag		type;char	   *dbname;			/* name of database to create */List	   *options;		/* List of DefElem nodes */
} CreatedbStmt;

语法定义(gram.y)：

CreatedbStmt:CREATE DATABASE name opt_with createdb_opt_list{CreatedbStmt *n = makeNode(CreatedbStmt);n->dbname = $3;	// 最重要的是告诉数据库，创建的数据库名是什么n->options = $5; // 创建数据库的一些选项，比如encoding, tablespace, location等等$$ = (Node *) n;};
执行层

CREATE DATABASE属于非优化语句，跳过优化器，直接进入执行器执行对应的操作。

exec_simple_query
--> pg_parse_query--> raw_parser
--> pg_analyze_and_rewrite--> parse_analyze--> transformStmt
--> pg_plan_queries
--> PortalStart
--> PortalRun--> PortalRunMulti--> ProcessUtility--> standard_ProcessUtility--> createdb		// 执行创建数据库操作
--> PortalDrop

下面是createdb函数的具体代码，其中一点需要注意，PG采用从模板数据库复制的方式来创建新的数据库，没有指定的话，默认模板是template1数据库。

创建数据库代码如下：

/* CREATE DATABASE */
Oid createdb(ParseState *pstate, const CreatedbStmt *stmt)
{Oid			src_dboid;Oid			src_owner;int			src_encoding = -1;char	   *src_collate = NULL;char	   *src_ctype = NULL;char	   *src_iculocale = NULL;char		src_locprovider = '\0';char	   *src_collversion = NULL;bool		src_istemplate;bool		src_allowconn;TransactionId src_frozenxid = InvalidTransactionId;MultiXactId src_minmxid = InvalidMultiXactId;Oid			src_deftablespace;volatile Oid dst_deftablespace;Relation	pg_database_rel;HeapTuple	tuple;Datum		new_record[Natts_pg_database];bool		new_record_nulls[Natts_pg_database];Oid			dboid = InvalidOid;Oid			datdba;ListCell   *option;DefElem    *dtablespacename = NULL;DefElem    *downer = NULL;DefElem    *dtemplate = NULL;DefElem    *dencoding = NULL;DefElem    *dlocale = NULL;DefElem    *dcollate = NULL;DefElem    *dctype = NULL;DefElem    *diculocale = NULL;DefElem    *dlocprovider = NULL;DefElem    *distemplate = NULL;DefElem    *dallowconnections = NULL;DefElem    *dconnlimit = NULL;DefElem    *dcollversion = NULL;DefElem    *dstrategy = NULL;char	   *dbname = stmt->dbname;char	   *dbowner = NULL;const char *dbtemplate = NULL;char	   *dbcollate = NULL;char	   *dbctype = NULL;char	   *dbiculocale = NULL;char		dblocprovider = '\0';char	   *canonname;int			encoding = -1;bool		dbistemplate = false;bool		dballowconnections = true;int			dbconnlimit = -1;char	   *dbcollversion = NULL;int			notherbackends;int			npreparedxacts;CreateDBStrategy dbstrategy = CREATEDB_WAL_LOG;createdb_failure_params fparms;/* Extract options from the statement node tree */foreach(option, stmt->options){DefElem    *defel = (DefElem *) lfirst(option);if (strcmp(defel->defname, "tablespace") == 0){if (dtablespacename)errorConflictingDefElem(defel, pstate);dtablespacename = defel;}else if (strcmp(defel->defname, "owner") == 0){if (downer)errorConflictingDefElem(defel, pstate);downer = defel;}else if (strcmp(defel->defname, "template") == 0){if (dtemplate)errorConflictingDefElem(defel, pstate);dtemplate = defel;}else if (strcmp(defel->defname, "encoding") == 0){if (dencoding)errorConflictingDefElem(defel, pstate);dencoding = defel;}else if (strcmp(defel->defname, "locale") == 0){if (dlocale)errorConflictingDefElem(defel, pstate);dlocale = defel;}else if (strcmp(defel->defname, "lc_collate") == 0){if (dcollate)errorConflictingDefElem(defel, pstate);dcollate = defel;}else if (strcmp(defel->defname, "lc_ctype") == 0){if (dctype)errorConflictingDefElem(defel, pstate);dctype = defel;}else if (strcmp(defel->defname, "icu_locale") == 0){if (diculocale)errorConflictingDefElem(defel, pstate);diculocale = defel;}else if (strcmp(defel->defname, "locale_provider") == 0){if (dlocprovider)errorConflictingDefElem(defel, pstate);dlocprovider = defel;}else if (strcmp(defel->defname, "is_template") == 0){if (distemplate)errorConflictingDefElem(defel, pstate);distemplate = defel;}else if (strcmp(defel->defname, "allow_connections") == 0){if (dallowconnections)errorConflictingDefElem(defel, pstate);dallowconnections = defel;}else if (strcmp(defel->defname, "connection_limit") == 0){if (dconnlimit)errorConflictingDefElem(defel, pstate);dconnlimit = defel;}else if (strcmp(defel->defname, "collation_version") == 0){if (dcollversion)errorConflictingDefElem(defel, pstate);dcollversion = defel;}else if (strcmp(defel->defname, "location") == 0){ereport(WARNING,(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),errmsg("LOCATION is not supported anymore"),errhint("Consider using tablespaces instead."),parser_errposition(pstate, defel->location)));}else if (strcmp(defel->defname, "oid") == 0){dboid = defGetObjectId(defel);/** We don't normally permit new databases to be created with* system-assigned OIDs. pg_upgrade tries to preserve database* OIDs, so we can't allow any database to be created with an OID* that might be in use in a freshly-initialized cluster created* by some future version. We assume all such OIDs will be from* the system-managed OID range.** As an exception, however, we permit any OID to be assigned when* allow_system_table_mods=on (so that initdb can assign system* OIDs to template0 and postgres) or when performing a binary* upgrade (so that pg_upgrade can preserve whatever OIDs it finds* in the source cluster).*/if (dboid < FirstNormalObjectId &&!allowSystemTableMods && !IsBinaryUpgrade)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE)),errmsg("OIDs less than %u are reserved for system objects", FirstNormalObjectId));}else if (strcmp(defel->defname, "strategy") == 0){if (dstrategy)errorConflictingDefElem(defel, pstate);dstrategy = defel;}elseereport(ERROR,(errcode(ERRCODE_SYNTAX_ERROR),errmsg("option \"%s\" not recognized", defel->defname),parser_errposition(pstate, defel->location)));}if (downer && downer->arg)dbowner = defGetString(downer);if (dtemplate && dtemplate->arg)dbtemplate = defGetString(dtemplate);if (dencoding && dencoding->arg){const char *encoding_name;if (IsA(dencoding->arg, Integer)){encoding = defGetInt32(dencoding);encoding_name = pg_encoding_to_char(encoding);if (strcmp(encoding_name, "") == 0 ||pg_valid_server_encoding(encoding_name) < 0)ereport(ERROR,(errcode(ERRCODE_UNDEFINED_OBJECT),errmsg("%d is not a valid encoding code",encoding),parser_errposition(pstate, dencoding->location)));}else{encoding_name = defGetString(dencoding);encoding = pg_valid_server_encoding(encoding_name);if (encoding < 0)ereport(ERROR,(errcode(ERRCODE_UNDEFINED_OBJECT),errmsg("%s is not a valid encoding name",encoding_name),parser_errposition(pstate, dencoding->location)));}}if (dlocale && dlocale->arg){dbcollate = defGetString(dlocale);dbctype = defGetString(dlocale);}if (dcollate && dcollate->arg)dbcollate = defGetString(dcollate);if (dctype && dctype->arg)dbctype = defGetString(dctype);if (diculocale && diculocale->arg)dbiculocale = defGetString(diculocale);if (dlocprovider && dlocprovider->arg){char	   *locproviderstr = defGetString(dlocprovider);if (pg_strcasecmp(locproviderstr, "icu") == 0)dblocprovider = COLLPROVIDER_ICU;else if (pg_strcasecmp(locproviderstr, "libc") == 0)dblocprovider = COLLPROVIDER_LIBC;elseereport(ERROR,(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),errmsg("unrecognized locale provider: %s",locproviderstr)));}if (distemplate && distemplate->arg)dbistemplate = defGetBoolean(distemplate);if (dallowconnections && dallowconnections->arg)dballowconnections = defGetBoolean(dallowconnections);if (dconnlimit && dconnlimit->arg){dbconnlimit = defGetInt32(dconnlimit);if (dbconnlimit < -1)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("invalid connection limit: %d", dbconnlimit)));}if (dcollversion)dbcollversion = defGetString(dcollversion);/* obtain OID of proposed owner */if (dbowner)datdba = get_role_oid(dbowner, false);elsedatdba = GetUserId();/** To create a database, must have createdb privilege and must be able to* become the target role (this does not imply that the target role itself* must have createdb privilege).  The latter provision guards against* "giveaway" attacks.  Note that a superuser will always have both of* these privileges a fortiori.*/if (!have_createdb_privilege())ereport(ERROR,(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),errmsg("permission denied to create database")));check_is_member_of_role(GetUserId(), datdba);/** Lookup database (template) to be cloned, and obtain share lock on it.* ShareLock allows two CREATE DATABASEs to work from the same template* concurrently, while ensuring no one is busy dropping it in parallel* (which would be Very Bad since we'd likely get an incomplete copy* without knowing it).  This also prevents any new connections from being* made to the source until we finish copying it, so we can be sure it* won't change underneath us.*/if (!dbtemplate)dbtemplate = "template1";	/* Default template database name */if (!get_db_info(dbtemplate, ShareLock,&src_dboid, &src_owner, &src_encoding,&src_istemplate, &src_allowconn,&src_frozenxid, &src_minmxid, &src_deftablespace,&src_collate, &src_ctype, &src_iculocale, &src_locprovider,&src_collversion))ereport(ERROR,(errcode(ERRCODE_UNDEFINED_DATABASE),errmsg("template database \"%s\" does not exist",dbtemplate)));/** Permission check: to copy a DB that's not marked datistemplate, you* must be superuser or the owner thereof.*/if (!src_istemplate){if (!pg_database_ownercheck(src_dboid, GetUserId()))ereport(ERROR,(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),errmsg("permission denied to copy database \"%s\"",dbtemplate)));}/* Validate the database creation strategy. */if (dstrategy && dstrategy->arg){char	   *strategy;strategy = defGetString(dstrategy);if (strcmp(strategy, "wal_log") == 0)dbstrategy = CREATEDB_WAL_LOG;else if (strcmp(strategy, "file_copy") == 0)dbstrategy = CREATEDB_FILE_COPY;elseereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("invalid create database strategy \"%s\"", strategy),errhint("Valid strategies are \"wal_log\", and \"file_copy\".")));}/* If encoding or locales are defaulted, use source's setting */if (encoding < 0)encoding = src_encoding;if (dbcollate == NULL)dbcollate = src_collate;if (dbctype == NULL)dbctype = src_ctype;if (dblocprovider == '\0')dblocprovider = src_locprovider;if (dbiculocale == NULL && dblocprovider == COLLPROVIDER_ICU)dbiculocale = src_iculocale;/* Some encodings are client only */if (!PG_VALID_BE_ENCODING(encoding))ereport(ERROR,(errcode(ERRCODE_WRONG_OBJECT_TYPE),errmsg("invalid server encoding %d", encoding)));/* Check that the chosen locales are valid, and get canonical spellings */if (!check_locale(LC_COLLATE, dbcollate, &canonname))ereport(ERROR,(errcode(ERRCODE_WRONG_OBJECT_TYPE),errmsg("invalid locale name: \"%s\"", dbcollate)));dbcollate = canonname;if (!check_locale(LC_CTYPE, dbctype, &canonname))ereport(ERROR,(errcode(ERRCODE_WRONG_OBJECT_TYPE),errmsg("invalid locale name: \"%s\"", dbctype)));dbctype = canonname;check_encoding_locale_matches(encoding, dbcollate, dbctype);if (dblocprovider == COLLPROVIDER_ICU){if (!(is_encoding_supported_by_icu(encoding)))ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("encoding \"%s\" is not supported with ICU provider",pg_encoding_to_char(encoding))));/** This would happen if template0 uses the libc provider but the new* database uses icu.*/if (!dbiculocale)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("ICU locale must be specified")));check_icu_locale(dbiculocale);}else{if (dbiculocale)ereport(ERROR,(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),errmsg("ICU locale cannot be specified unless locale provider is ICU")));}/** Check that the new encoding and locale settings match the source* database.  We insist on this because we simply copy the source data ---* any non-ASCII data would be wrongly encoded, and any indexes sorted* according to the source locale would be wrong.** However, we assume that template0 doesn't contain any non-ASCII data* nor any indexes that depend on collation or ctype, so template0 can be* used as template for creating a database with any encoding or locale.*/if (strcmp(dbtemplate, "template0") != 0){if (encoding != src_encoding)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("new encoding (%s) is incompatible with the encoding of the template database (%s)",pg_encoding_to_char(encoding),pg_encoding_to_char(src_encoding)),errhint("Use the same encoding as in the template database, or use template0 as template.")));if (strcmp(dbcollate, src_collate) != 0)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("new collation (%s) is incompatible with the collation of the template database (%s)",dbcollate, src_collate),errhint("Use the same collation as in the template database, or use template0 as template.")));if (strcmp(dbctype, src_ctype) != 0)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("new LC_CTYPE (%s) is incompatible with the LC_CTYPE of the template database (%s)",dbctype, src_ctype),errhint("Use the same LC_CTYPE as in the template database, or use template0 as template.")));if (dblocprovider != src_locprovider)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("new locale provider (%s) does not match locale provider of the template database (%s)",collprovider_name(dblocprovider), collprovider_name(src_locprovider)),errhint("Use the same locale provider as in the template database, or use template0 as template.")));if (dblocprovider == COLLPROVIDER_ICU){Assert(dbiculocale);Assert(src_iculocale);if (strcmp(dbiculocale, src_iculocale) != 0)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("new ICU locale (%s) is incompatible with the ICU locale of the template database (%s)",dbiculocale, src_iculocale),errhint("Use the same ICU locale as in the template database, or use template0 as template.")));}}/** If we got a collation version for the template database, check that it* matches the actual OS collation version.  Otherwise error; the user* needs to fix the template database first.  Don't complain if a* collation version was specified explicitly as a statement option; that* is used by pg_upgrade to reproduce the old state exactly.** (If the template database has no collation version, then either the* platform/provider does not support collation versioning, or it's* template0, for which we stipulate that it does not contain* collation-using objects.)*/if (src_collversion && !dcollversion){char	   *actual_versionstr;actual_versionstr = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);if (!actual_versionstr)ereport(ERROR,(errmsg("template database \"%s\" has a collation version, but no actual collation version could be determined",dbtemplate)));if (strcmp(actual_versionstr, src_collversion) != 0)ereport(ERROR,(errmsg("template database \"%s\" has a collation version mismatch",dbtemplate),errdetail("The template database was created using collation version %s, ""but the operating system provides version %s.",src_collversion, actual_versionstr),errhint("Rebuild all objects in the template database that use the default collation and run ""ALTER DATABASE %s REFRESH COLLATION VERSION, ""or build PostgreSQL with the right library version.",quote_identifier(dbtemplate))));}if (dbcollversion == NULL)dbcollversion = src_collversion;/** Normally, we copy the collation version from the template database.* This last resort only applies if the template database does not have a* collation version, which is normally only the case for template0.*/if (dbcollversion == NULL)dbcollversion = get_collation_actual_version(dblocprovider, dblocprovider == COLLPROVIDER_ICU ? dbiculocale : dbcollate);/* Resolve default tablespace for new database */if (dtablespacename && dtablespacename->arg){char	   *tablespacename;AclResult	aclresult;tablespacename = defGetString(dtablespacename);dst_deftablespace = get_tablespace_oid(tablespacename, false);/* check permissions */aclresult = pg_tablespace_aclcheck(dst_deftablespace, GetUserId(),ACL_CREATE);if (aclresult != ACLCHECK_OK)aclcheck_error(aclresult, OBJECT_TABLESPACE,tablespacename);/* pg_global must never be the default tablespace */if (dst_deftablespace == GLOBALTABLESPACE_OID)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE),errmsg("pg_global cannot be used as default tablespace")));/** If we are trying to change the default tablespace of the template,* we require that the template not have any files in the new default* tablespace.  This is necessary because otherwise the copied* database would contain pg_class rows that refer to its default* tablespace both explicitly (by OID) and implicitly (as zero), which* would cause problems.  For example another CREATE DATABASE using* the copied database as template, and trying to change its default* tablespace again, would yield outright incorrect results (it would* improperly move tables to the new default tablespace that should* stay in the same tablespace).*/if (dst_deftablespace != src_deftablespace){char	   *srcpath;struct stat st;srcpath = GetDatabasePath(src_dboid, dst_deftablespace);if (stat(srcpath, &st) == 0 &&S_ISDIR(st.st_mode) &&!directory_is_empty(srcpath))ereport(ERROR,(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),errmsg("cannot assign new default tablespace \"%s\"",tablespacename),errdetail("There is a conflict because database \"%s\" already has some tables in this tablespace.",dbtemplate)));pfree(srcpath);}}else{/* Use template database's default tablespace */dst_deftablespace = src_deftablespace;/* Note there is no additional permission check in this path */}/** If built with appropriate switch, whine when regression-testing* conventions for database names are violated.  But don't complain during* initdb.*/
#ifdef ENFORCE_REGRESSION_TEST_NAME_RESTRICTIONSif (IsUnderPostmaster && strstr(dbname, "regression") == NULL)elog(WARNING, "databases created by regression test cases should have names including \"regression\"");
#endif/** Check for db name conflict.  This is just to give a more friendly error* message than "unique index violation".  There's a race condition but* we're willing to accept the less friendly message in that case.*/if (OidIsValid(get_database_oid(dbname, true)))ereport(ERROR,(errcode(ERRCODE_DUPLICATE_DATABASE),errmsg("database \"%s\" already exists", dbname)));/** The source DB can't have any active backends, except this one* (exception is to allow CREATE DB while connected to template1).* Otherwise we might copy inconsistent data.** This should be last among the basic error checks, because it involves* potential waiting; we may as well throw an error first if we're gonna* throw one.*/if (CountOtherDBBackends(src_dboid, &notherbackends, &npreparedxacts))ereport(ERROR,(errcode(ERRCODE_OBJECT_IN_USE),errmsg("source database \"%s\" is being accessed by other users",dbtemplate),errdetail_busy_db(notherbackends, npreparedxacts)));/** Select an OID for the new database, checking that it doesn't have a* filename conflict with anything already existing in the tablespace* directories.*/pg_database_rel = table_open(DatabaseRelationId, RowExclusiveLock);/** If database OID is configured, check if the OID is already in use or* data directory already exists.*/if (OidIsValid(dboid)){char	   *existing_dbname = get_database_name(dboid);if (existing_dbname != NULL)ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE)),errmsg("database OID %u is already in use by database \"%s\"",dboid, existing_dbname));if (check_db_file_conflict(dboid))ereport(ERROR,(errcode(ERRCODE_INVALID_PARAMETER_VALUE)),errmsg("data directory with the specified OID %u already exists", dboid));}else{/* Select an OID for the new database if is not explicitly configured. */do{dboid = GetNewOidWithIndex(pg_database_rel, DatabaseOidIndexId,Anum_pg_database_oid);} while (check_db_file_conflict(dboid));}/** Insert a new tuple into pg_database.  This establishes our ownership of* the new database name (anyone else trying to insert the same name will* block on the unique index, and fail after we commit).*/Assert((dblocprovider == COLLPROVIDER_ICU && dbiculocale) ||(dblocprovider != COLLPROVIDER_ICU && !dbiculocale));/* Form tuple */MemSet(new_record, 0, sizeof(new_record));MemSet(new_record_nulls, false, sizeof(new_record_nulls));new_record[Anum_pg_database_oid - 1] = ObjectIdGetDatum(dboid);new_record[Anum_pg_database_datname - 1] =DirectFunctionCall1(namein, CStringGetDatum(dbname));new_record[Anum_pg_database_datdba - 1] = ObjectIdGetDatum(datdba);new_record[Anum_pg_database_encoding - 1] = Int32GetDatum(encoding);new_record[Anum_pg_database_datlocprovider - 1] = CharGetDatum(dblocprovider);new_record[Anum_pg_database_datistemplate - 1] = BoolGetDatum(dbistemplate);new_record[Anum_pg_database_datallowconn - 1] = BoolGetDatum(dballowconnections);new_record[Anum_pg_database_datconnlimit - 1] = Int32GetDatum(dbconnlimit);new_record[Anum_pg_database_datfrozenxid - 1] = TransactionIdGetDatum(src_frozenxid);new_record[Anum_pg_database_datminmxid - 1] = TransactionIdGetDatum(src_minmxid);new_record[Anum_pg_database_dattablespace - 1] = ObjectIdGetDatum(dst_deftablespace);new_record[Anum_pg_database_datcollate - 1] = CStringGetTextDatum(dbcollate);new_record[Anum_pg_database_datctype - 1] = CStringGetTextDatum(dbctype);if (dbiculocale)new_record[Anum_pg_database_daticulocale - 1] = CStringGetTextDatum(dbiculocale);elsenew_record_nulls[Anum_pg_database_daticulocale - 1] = true;if (dbcollversion)new_record[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(dbcollversion);elsenew_record_nulls[Anum_pg_database_datcollversion - 1] = true;/** We deliberately set datacl to default (NULL), rather than copying it* from the template database.  Copying it would be a bad idea when the* owner is not the same as the template's owner.*/new_record_nulls[Anum_pg_database_datacl - 1] = true;tuple = heap_form_tuple(RelationGetDescr(pg_database_rel),new_record, new_record_nulls);CatalogTupleInsert(pg_database_rel, tuple);/** Now generate additional catalog entries associated with the new DB*//* Register owner dependency */recordDependencyOnOwner(DatabaseRelationId, dboid, datdba);/* Create pg_shdepend entries for objects within database */copyTemplateDependencies(src_dboid, dboid);/* Post creation hook for new database */InvokeObjectPostCreateHook(DatabaseRelationId, dboid, 0);/** If we're going to be reading data for the to-be-created database into* shared_buffers, take a lock on it. Nobody should know that this* database exists yet, but it's good to maintain the invariant that a* lock an AccessExclusiveLock on the database is sufficient to drop all* of its buffers without worrying about more being read later.** Note that we need to do this before entering the* PG_ENSURE_ERROR_CLEANUP block below, because createdb_failure_callback* expects this lock to be held already.*/if (dbstrategy == CREATEDB_WAL_LOG)LockSharedObject(DatabaseRelationId, dboid, 0, AccessShareLock);/** Once we start copying subdirectories, we need to be able to clean 'em* up if we fail.  Use an ENSURE block to make sure this happens.  (This* is not a 100% solution, because of the possibility of failure during* transaction commit after we leave this routine, but it should handle* most scenarios.)*/fparms.src_dboid = src_dboid;fparms.dest_dboid = dboid;fparms.strategy = dbstrategy;PG_ENSURE_ERROR_CLEANUP(createdb_failure_callback,PointerGetDatum(&fparms));{/** If the user has asked to create a database with WAL_LOG strategy* then call CreateDatabaseUsingWalLog, which will copy the database* at the block level and it will WAL log each copied block.* Otherwise, call CreateDatabaseUsingFileCopy that will copy the* database file by file.*/if (dbstrategy == CREATEDB_WAL_LOG)CreateDatabaseUsingWalLog(src_dboid, dboid, src_deftablespace,dst_deftablespace);elseCreateDatabaseUsingFileCopy(src_dboid, dboid, src_deftablespace,dst_deftablespace);/** Close pg_database, but keep lock till commit.*/table_close(pg_database_rel, NoLock);/** Force synchronous commit, thus minimizing the window between* creation of the database files and committal of the transaction. If* we crash before committing, we'll have a DB that's taking up disk* space but is not in pg_database, which is not good.*/ForceSyncCommit();}PG_END_ENSURE_ERROR_CLEANUP(createdb_failure_callback,PointerGetDatum(&fparms));return dboid;
}

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