PostgreSQL启动过程中的那些事三:加载GUC参数
1先上个图,看一下函数调用过程梗概,中间细节有略
GUC参数初始化分两步,第一步先读取buildin/compiled-in的GUC参数默认值,这里包括全部的GUC参数,建立GUC参数相关结构变量,第二步读取postgresql.conf配置文件中的参数设置之。从上图中能看出来,这个读取并设置postgresql.conf中参数的过程还是挺复杂的。
2初始化GUC相关数据结构并取hardcode/buildin的参数值。 pg里的GUC参数按设置的值分五种类型,分别是bool、int、real、string、enum,根据这五种类型,定义了五种结构类型,再根据这五种结构,每个类型建一个对应的静态数组,用于存储这些相应类型的GUC参数。这五种类型是config_bool、config_int、config_real、config_string、config_enum,对应的静态数组是ConfigureNamesBool、ConfigureNamesInt、ConfigureNamesReal、ConfigureNamesString、ConfigureNamesEnum。具体结构和数组定义见下面。 五个结构定义: struct config_bool { struct config_generic gen; /* these fields must be set correctly in initial value: */ /* (all but reset_val are constants) */ bool *variable; bool boot_val; GucIntCheckHookcheck_hook; GucBoolAssignHookassign_hook; GucShowHookshow_hook; /* variable fields,initialized at runtime: */ bool reset_val; void * reset_extra }; struct config_int { struct config_generic gen; /*constant fields,must be set correctly in initial value: */ int *variable; int boot_val; int min; int max; GucIntCheckHookcheck_hook; GucIntAssignHookassign_hook; GucShowHookshow_hook; /* variable fields,initialized at runtime: */ int reset_val; void * reset_extra }; struct config_real { struct config_generic gen; /* constantfields,must be set correctly in initial value: */ double *variable; double boot_val; double min; double max; GucIntCheckHookcheck_hook; GucRealAssignHookassign_hook; GucShowHookshow_hook; /* variable fields,initialized at runtime: */ double reset_val; void * reset_extra }; struct config_string { struct config_generic gen; /* constant fields,must beset correctly in initial value: */ char **variable; const char *boot_val; GucIntCheckHookcheck_hook; GucStringAssignHookassign_hook; GucShowHookshow_hook; /* variable fields,initialized at runtime: */ char *reset_val; void * reset_extra }; struct config_enum { struct config_generic gen; /* constant fields,must beset correctly in initial value: */ int *variable; int boot_val; GucIntCheckHookcheck_hook; GucStringAssignHookassign_hook; GucShowHookshow_hook; /* variable fields,initialized at runtime: */ int reset_val; void * reset_extra }; 和结构类型对应的五个静态数组: static struct config_boolConfigureNamesBool[] = { { {"enable_seqscan",PGC_USERSET,QUERY_TUNING_METHOD, gettext_noop("Enablesthe planner's use of sequential-scan plans."), NULL }, &enable_seqscan, true, NULL,NULL,NULL }, …… /*End-of-list marker */ { {NULL,NULL},false,NULL } }; static struct config_int ConfigureNamesInt[]= { { {"archive_timeout",PGC_SIGHUP,WAL_ARCHIVING, gettext_noop("Forcesa switch to the next xlog file if a " "new file has not been started within Nseconds."), GUC_UNIT_S }, &XLogArchiveTimeout, 0,INT_MAX,NULL } }; static struct config_realConfigureNamesReal[] = { { {"seq_page_cost",QUERY_TUNING_COST, gettext_noop("Setsthe planner's estimate of the cost of a " "sequentially fetched disk page."), &seq_page_cost, DEFAULT_SEQ_PAGE_COST,DBL_MAX, /*End-of-list marker */ { {NULL,0.0,NULL } }; static struct config_stringConfigureNamesString[] = { { {"archive_command", gettext_noop("Setsthe shell command that will be called to archive a WAL file."), &XLogArchiveCommand, "",show_archive_command },NULL } }; static struct config_enumConfigureNamesEnum[] = { { {"backslash_quote",COMPAT_OPTIONS_PREVIOUS, gettext_noop("Setswhether "'" is allowed in string literals."), &backslash_quote, BACKSLASH_QUOTE_SAFE_ENCODING,backslash_quote_options,NULL } }; 上面五个结构定义中,每个结构的第一个成员变量都是一个config_generic结构的gen成员,下面是config_generic的结构定义: struct config_generic { /* constantfields,must be set correctly in initial value: */ const char *name; /* name of variable - MUST BE FIRST */ GucContext context; /* context required to set the variable */ enumconfig_group group; /* to help organize variables by function */ const char *short_desc; /* short desc. of this variable's purpose */ const char *long_desc; /* long desc. of this variable's purpose */ int flags; /* flag bits,see below*/ /* variablefields,initialized at runtime: */ enumconfig_type vartype; /* type of variable (set only at startup) */ int status; /* status bits,see below*/ GucSource reset_source; /* source of thereset_value */ GucSource source; /*source of the current actual value */ GucStack*stack; /* stacked outside-of-transaction states */ void *extra; /*"extra" pointer for current actual value */ char *sourcefile; /* filecurrent setting is from (NULL if not * file) */ int sourceline; /* line in source file */ }; 然后,定义一个config_generic **类型的静态变量数组guc_variables,再计算参数总数,所有参数以config_generic*类型计算所需内存空间,冗余25%内存后malloc分配内存空间。把guc_variables每一个元素指向ConfigureNamesBool、ConfigureNamesInt、ConfigureNamesReal、ConfigureNamesString、ConfigureNamesEnum这五个数组的config_generic类型成员gen的地址,然后按照参数名称把所有元素做了快速排序。这个过程中还设置了一些GUC参数的默认值。 static struct config_generic **guc_variables; 后面查询GUC参数都是在guc_variables这个已排序的数组里找。这样GUC参数的数据结构就搭建完成了,下面看看GUC参数相关的数据结构图吧。 先把涉及到的结构的图分别列出,再画个这些结构的组织关系示意图。
3加载postgresql.conf参数配置文件里的参数设置 从main->PostmasterMain->SelectConfigFiles->ProcessConfigFile开始处理参数配置文件postgresql.conf,读取postgresql.conf配置文件的调用过程是ProcessConfigFile -> ParseConfigFile -> AllocateFile->fopen,最后用fopen打开文件,其中ProcessConfigFile、ParseConfigFile在文件srcbackendutilsmiscguc-file.l中,AllocateFile在文件srcbackendstoragefilefd.c中。 pg使用 flex 去处理 conf 文件。在ParseConfigFile中把配置文件中的配置项组织成一个链表,调用set_config_option检查这些值是否有效,若可以设置就调用set_config_option设置这些值。 这里以"max_connections"做例子,从配置文件读取"max_connections",然后从guc_variables数组中找元素" max_connections ",比较参数结构的GucContext (枚举类参数能被设置的时机。定义见下面)枚举类型成员context和当前时间,看是否可以此刻修改。接着比较参数结构的GucSource(枚举了当前GUC参数设置的来源。除非参数新值的来源等级不小于原参数的来源等级时,新设置才能生效。例如,修改配置文件不能覆盖postmaster command line的设置。定义见下面)枚举类型成员source和新参数值的来源,看是否可以修改。如果可以,把config_generic结构类型的元素" max_connections "类型转换为config_int类型,修改variable成员为新值,修改该参数的来源source为当前来源PGC_S_FILE,如果元素" max_connections "的reset_source <= source,修改reset_val成员为新值,修改该参数的reset_source为当前来源PGC_S_FILE。 typedef enum { PGC_INTERNAL, PGC_POSTMASTER, PGC_SIGHUP, PGC_BACKEND, PGC_SUSET, PGC_USERSET } GucContext; typedef enum { PGC_S_DEFAULT,/*wired-in default */ PGC_S_ENV_VAR,/*postmaster environment variable */ PGC_S_FILE,/*postgresql.conf */ PGC_S_ARGV,/*postmaster command line */ PGC_S_DATABASE,/*per-database setting */ PGC_S_USER,/*per-user setting */ PGC_S_CLIENT,/* fromclient connection request */ PGC_S_OVERRIDE,/*special case to forcibly set default */ PGC_S_INTERACTIVE,/* dividingline for error reporting */ PGC_S_TEST,/*test per-database or per-user setting */ PGC_S_SESSION /* SETcommand */ } GucSource (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |