What is the implementation logic of PostgresMain function in PostgreSQL?

< numParams; i++) paramTypes[i] = pq_getmsgint(&input_message, 4); } pq_getmsgend(&input_message); exec_parse_message(query_string, stmt_name, paramTypes, numParams); } break; case 'B': /* bind */ forbidden_in_wal_sender(firstchar); /* Set statement_timestamp() */ SetCurrentStatementStartTimestamp(); /* * this message is complex enough that it seems best to put * the field extraction out-of-line */ exec_bind_message(&input_message); break; case 'E': /* execute */ { const char *portal_name; int max_rows; forbidden_in_wal_sender(firstchar); /* Set statement_timestamp() */ SetCurrentStatementStartTimestamp(); portal_name = pq_getmsgstring(&input_message); max_rows = pq_getmsgint(&input_message, 4); pq_getmsgend(&input_message); exec_execute_message(portal_name, max_rows); } break; case 'F': /* fastpath function call */ forbidden_in_wal_sender(firstchar); /* Set statement_timestamp() */ SetCurrentStatementStartTimestamp(); /* Report query to various monitoring facilities. */ pgstat_report_activity(STATE_FASTPATH, NULL); set_ps_display("", false); /* start an xact for this function invocation */ start_xact_command(); /* * Note: we may at this point be inside an aborted * transaction. We can't throw error for that until we've * finished reading the function-call message, so * HandleFunctionRequest() must check for it after doing so. * Be careful not to do anything that assumes we're inside a * valid transaction here. */ /* switch back to message context */ MemoryContextSwitchTo(MessageContext); HandleFunctionRequest(&input_message); /* commit the function-invocation transaction */ finish_xact_command(); send_ready_for_query = true; break; case 'C': /* close */ { int close_type; const char *close_target; forbidden_in_wal_sender(firstchar); close_type = pq_getmsgbyte(&input_message); close_target = pq_getmsgstring(&input_message); pq_getmsgend(&input_message); switch (close_type) { case 'S': if (close_target[0] != '\0') DropPreparedStatement(close_target, false); else { /* special-case the unnamed statement */ drop_unnamed_stmt(); } break; case 'P': { Portal portal; portal = GetPortalByName(close_target); if (PortalIsValid(portal)) PortalDrop(portal, false); } break; default: ereport(ERROR, (errcode(ERRCODE_PROTOCOL_VIOLATION), errmsg("invalid CLOSE message subtype %d", close_type))); break; } if (whereToSendOutput == DestRemote) pq_putemptymessage('3'); /* CloseComplete */ } break; case 'D': /* describe */ { int describe_type; const char *describe_target; forbidden_in_wal_sender(firstchar); /* Set statement_timestamp() (needed for xact) */ SetCurrentStatementStartTimestamp(); describe_type = pq_getmsgbyte(&input_message); describe_target = pq_getmsgstring(&input_message); pq_getmsgend(&input_message); switch (describe_type) { case 'S': exec_describe_statement_message(describe_target); break; case 'P': exec_describe_portal_message(describe_target); break; default: ereport(ERROR, (errcode(ERRCODE_PROTOCOL_VIOLATION), errmsg("invalid DESCRIBE message subtype %d", describe_type))); break; } } break; case 'H': /* flush */ pq_getmsgend(&input_message); if (whereToSendOutput == DestRemote) pq_flush(); break; case 'S': /* sync */ pq_getmsgend(&input_message); finish_xact_command(); send_ready_for_query = true; break; /* * 'X' means that the frontend is closing down the socket. EOF * means unexpected loss of frontend connection. Either way, * perform normal shutdown. */ case 'X': case EOF: /* * Reset whereToSendOutput to prevent ereport from attempting * to send any more messages to client. */ if (whereToSendOutput == DestRemote) whereToSendOutput = DestNone; /* * NOTE: if you are tempted to add more code here, DON'T! * Whatever you had in mind to do should be set up as an * on_proc_exit or on_shmem_exit callback, instead. Otherwise * it will fail to be called during other backend-shutdown * scenarios. */ proc_exit(0); case 'd': /* copy data */ case 'c': /* copy done */ case 'f': /* copy fail */ /* * Accept but ignore these messages, per protocol spec; we * probably got here because a COPY failed, and the frontend * is still sending data. */ break; default: ereport(FATAL, (errcode(ERRCODE_PROTOCOL_VIOLATION), errmsg("invalid frontend message type %d", firstchar))); } } /* end of input-reading loop */}二、基础信息 PostgresMain函数使用的数据结构、宏定义以及依赖的函数等。 数据结构/宏定义 1、StringInfoData /*------------------------- * StringInfoData holds information about an extensible string. * data is the current buffer for the string (allocated with palloc). * len is the current string length. There is guaranteed to be * a terminating '\0' at data[len], although this is not very * useful when the string holds binary data rather than text. * maxlen is the allocated size in bytes of 'data', i.e. the maximum * string size (including the terminating '\0' char) that we can * currently store in 'data' without having to reallocate * more space. We must always have maxlen >

Len. * cursor is initialized to zero by makeStringInfo or initStringInfo, * but is not otherwise touched by the stringinfo.c routines. * Some routines use it to scan through a StringInfo. *-* / typedef struct StringInfoData {char * data; int len; int maxlen; int cursor;} StringInfoData; typedef StringInfoData * StringInfo

2. Macro definition

# ifndef WIN32 # define PG_SETMASK (mask) sigprocmask (SIG_SETMASK, mask, NULL) # else / * Emulate POSIX sigset_t APIs on Windows * / typedef int sigset_t; extern int pqsigsetmask (int mask) # define PG_SETMASK (mask) pqsigsetmask (* (mask)) # define sigemptyset (set) (* (set) = 0) # define sigfillset (set) (* (set) = ~ 0) # define sigaddset (set, signum) (* (set) | = (sigmask (signum) # define sigdelset (set, signum) (* (set) & = ~ (sigmask (signum) # endif / * WIN32 * /

3. Global variables

/ * IsPostmasterEnvironment is true in a postmaster process and any postmaster * child process; it is false in a standalone process (bootstrap or * standalone backend). IsUnderPostmaster is true in postmaster child * processes. Note that "child process" includes all children, not only * regular backends. These should be set correctly as early as possible * in the execution of a process, so that error handling will do the right * things if an error should occur during process initialization. * * These are initialized for the bootstrap/standalone case. * / bool IsPostmasterEnvironment = false; bool IsUnderPostmaster = false; bool IsBinaryUpgrade = false; bool IsBackgroundWorker = false; bool am_walsender = false; / * Am I a walsender process? *

Dependent function

1 、 InitStandaloneProcess

/ * Initialize the basic environment for a standalone process. * * argv0 has to be suitable to find the program's executable. * / void InitStandaloneProcess (const char * argv0) {Assert (! IsPostmasterEnvironment); MyProcPid = getpid (); / * reset MyProcPid * / MyStartTime = time (NULL); / * set our start time in case we call elog * / / * Initialize process-local latch support * / InitializeLatchSupport (); MyLatch = & LocalLatchData; InitLatch (MyLatch) / * Compute paths, no postmaster to inherit from * / if (my_exec_path [0] = ='\ 0') {if (find_my_exec (argv0, my_exec_path)

< 0) elog(FATAL, "%s: could not locate my own executable path", argv0); } if (pkglib_path[0] == '\0') get_pkglib_path(my_exec_path, pkglib_path); } 2、InitializeGUCOptions /* * Initialize GUC options during program startup. * * Note that we cannot read the config file yet, since we have not yet * processed command-line switches. */ void InitializeGUCOptions(void) { int i; /* * Before log_line_prefix could possibly receive a nonempty setting, make * sure that timezone processing is minimally alive (see elog.c). */ pg_timezone_initialize(); /* * Build sorted array of all GUC variables. */ build_guc_variables(); /* * Load all variables with their compiled-in defaults, and initialize * status fields as needed. */ for (i = 0; i < num_guc_variables; i++) { InitializeOneGUCOption(guc_variables[i]); } guc_dirty = false; reporting_enabled = false; /* * Prevent any attempt to override the transaction modes from * non-interactive sources. */ SetConfigOption("transaction_isolation", "default", PGC_POSTMASTER, PGC_S_OVERRIDE); SetConfigOption("transaction_read_only", "no", PGC_POSTMASTER, PGC_S_OVERRIDE); SetConfigOption("transaction_deferrable", "no", PGC_POSTMASTER, PGC_S_OVERRIDE); /* * For historical reasons, some GUC parameters can receive defaults from * environment variables. Process those settings. */ InitializeGUCOptionsFromEnvironment(); } 3、process_postgres_switches /* ---------------------------------------------------------------- * process_postgres_switches * Parse command line arguments for PostgresMain * * This is called twice, once for the "secure" options coming from the * postmaster or command line, and once for the "insecure" options coming * from the client's startup packet. The latter have the same syntax but * may be restricted in what they can do. * * argv[0] is ignored in either case (it's assumed to be the program name). * * ctx is PGC_POSTMASTER for secure options, PGC_BACKEND for insecure options * coming from the client, or PGC_SU_BACKEND for insecure options coming from * a superuser client. * * If a database name is present in the command line arguments, it's * returned into *dbname (this is allowed only if *dbname is initially NULL). * ---------------------------------------------------------------- */ void process_postgres_switches(int argc, char *argv[], GucContext ctx, const char **dbname) { bool secure = (ctx == PGC_POSTMASTER); int errs = 0; GucSource gucsource; int flag; if (secure) { gucsource = PGC_S_ARGV; /* switches came from command line */ /* Ignore the initial --single argument, if present */ if (argc >

< NUM_LOCK_PARTITIONS; i++) Assert(SHMQueueEmpty(&(MyProc->