PostgreSQL在何处处理 sql查询之二

在exec_simple_query中，代码如下：

/*
 * exec_simple_query
 *
 * Execute a "simple Query" protocol message.
 */
static void
exec_simple_query(const char *query_string)
{
    CommandDest dest = whereToSendOutput;
    MemoryContext oldcontext;
    List       *parsetree_list;
    ListCell   *parsetree_item;


    bool        save_log_statement_stats = log_statement_stats;
    bool        was_logged = false;
    bool        isTopLevel;
    char        msec_str[32];


    /*
     * Report query to various monitoring facilities.
     */
    debug_query_string = query_string;

    pgstat_report_activity(STATE_RUNNING, query_string);

    TRACE_POSTGRESQL_QUERY_START(query_string);

    /*
     * We use save_log_statement_stats so ShowUsage doesn't report incorrect
     * results because ResetUsage wasn't called.
     */
    if (save_log_statement_stats)
        ResetUsage();

    /*
     * Start up a transaction command.    All queries generated by the
     * query_string will be in this same command block, *unless* we find a
     * BEGIN/COMMIT/ABORT statement; we have to force a new xact command after
     * one of those, else bad things will happen in xact.c. (Note that this
     * will normally change current memory context.)
     */
    start_xact_command();

    /*
     * Zap any pre-existing unnamed statement.    (While not strictly necessary,
     * it seems best to define simple-Query mode as if it used the unnamed
     * statement and portal; this ensures we recover any storage used by prior
     * unnamed operations.)
     */
    drop_unnamed_stmt();

    /*
     * Switch to appropriate context for constructing parsetrees.
     */
    oldcontext = MemoryContextSwitchTo(MessageContext);

    /*
     * Do basic parsing of the query or queries (this should be safe even if
     * we are in aborted transaction state!)
     */
    parsetree_list = pg_parse_query(query_string);

    /* Log immediately if dictated by log_statement */
    if (check_log_statement(parsetree_list))
    {
        ereport(LOG,
                (errmsg("statement: %s", query_string),
                 errhidestmt(true),
                 errdetail_execute(parsetree_list)));
        was_logged = true;
    }

    /*
     * Switch back to transaction context to enter the loop.
     */
    MemoryContextSwitchTo(oldcontext);

    /*
     * We'll tell PortalRun it's a top-level command iff there's exactly one
     * raw parsetree.  If more than one, it's effectively a transaction block
     * and we want PreventTransactionChain to reject unsafe commands. (Note:
     * we're assuming that query rewrite cannot add commands that are
     * significant to PreventTransactionChain.)
     */
    isTopLevel = (list_length(parsetree_list) == 1);

    /*
     * Run through the raw parsetree(s) and process each one.
     */
    foreach(parsetree_item, parsetree_list)
    {
        Node       *parsetree = (Node *) lfirst(parsetree_item);

        bool        snapshot_set = false;
        const char *commandTag;
        char        completionTag[COMPLETION_TAG_BUFSIZE];
        List       *querytree_list,
                   *plantree_list;
        Portal        portal;
        DestReceiver *receiver;
        int16        format;

        /*
         * Get the command name for use in status display (it also becomes the
         * default completion tag, down inside PortalRun).    Set ps_status and
         * do any special start-of-SQL-command processing needed by the
         * destination.
         */
        commandTag = CreateCommandTag(parsetree);

        //fprintf(stderr,"commandTag is :%s\n",commandTag);

        set_ps_display(commandTag, false);

        BeginCommand(commandTag, dest);

        //fprintf(stderr,"BeginCommand finished.\n");

        /*
         * If we are in an aborted transaction, reject all commands except
         * COMMIT/ABORT.  It is important that this test occur before we try
         * to do parse analysis, rewrite, or planning, since all those phases
         * try to do database accesses, which may fail in abort state. (It
         * might be safe to allow some additional utility commands in this
         * state, but not many...)
         */
        if (IsAbortedTransactionBlockState() &&
            !IsTransactionExitStmt(parsetree))
            ereport(ERROR,
                    (errcode(ERRCODE_IN_FAILED_SQL_TRANSACTION),
                     errmsg("current transaction is aborted, "
                          "commands ignored until end of transaction block"),
                     errdetail_abort()));

        /* Make sure we are in a transaction command */
        start_xact_command();

        /* If we got a cancel signal in parsing or prior command, quit */
        CHECK_FOR_INTERRUPTS();

        /*
         * Set up a snapshot if parse analysis/planning will need one.
         */
        if (analyze_requires_snapshot(parsetree))
        {
            PushActiveSnapshot(GetTransactionSnapshot());
            snapshot_set = true;
        }

        /*
         * OK to analyze, rewrite, and plan this query.
         *
         * Switch to appropriate context for constructing querytrees (again,
         * these must outlive the execution context).
         */
        oldcontext = MemoryContextSwitchTo(MessageContext);

        querytree_list = pg_analyze_and_rewrite(parsetree, query_string,
                                                NULL, 0);

        plantree_list = pg_plan_queries(querytree_list, 0, NULL);

        /* If we got a cancel signal in analysis or planning, quit */
        CHECK_FOR_INTERRUPTS();

        /*
         * Create unnamed portal to run the query or queries in. If there
         * already is one, silently drop it.
         */
        portal = CreatePortal("", true, true);
        /* Don't display the portal in pg_cursors */
        portal->visible = false;

        /*
         * We don't have to copy anything into the portal, because everything
         * we are passing here is in MessageContext, which will outlive the
         * portal anyway.
         */
        PortalDefineQuery(portal,
                          NULL,
                          query_string,
                          commandTag,
                          plantree_list,
                          NULL);

        /*
         * Start the portal.
         *
         * If we took a snapshot for parsing/planning, the portal may be able
         * to reuse it for the execution phase.  Currently, this will only
         * happen in PORTAL_ONE_SELECT mode.  But even if PortalStart doesn't
         * end up being able to do this, keeping the parse/plan snapshot
         * around until after we start the portal doesn't cost much.
         */
        PortalStart(portal, NULL, 0, snapshot_set);

        /* Done with the snapshot used for parsing/planning */
        if (snapshot_set)
            PopActiveSnapshot();

        /*
         * Select the appropriate output format: text unless we are doing a
         * FETCH from a binary cursor.    (Pretty grotty to have to do this here
         * --- but it avoids grottiness in other places.  Ah, the joys of
         * backward compatibility...)
         */
        format = 0;                /* TEXT is default */
        if (IsA(parsetree, FetchStmt))
        {
            FetchStmt  *stmt = (FetchStmt *) parsetree;

            if (!stmt->ismove)
            {
                Portal        fportal = GetPortalByName(stmt->portalname);

                if (PortalIsValid(fportal) &&
                    (fportal->cursorOptions & CURSOR_OPT_BINARY))
                    format = 1; /* BINARY */
            }
        }
        PortalSetResultFormat(portal, 1, &format);

        /*
         * Now we can create the destination receiver object.
         */
        receiver = CreateDestReceiver(dest);
        if (dest == DestRemote)
            SetRemoteDestReceiverParams(receiver, portal);

        /*
         * Switch back to transaction context for execution.
         */
        MemoryContextSwitchTo(oldcontext);

        /*
         * Run the portal to completion, and then drop it (and the receiver).
         */
        (void) PortalRun(portal,
                         FETCH_ALL,
                         isTopLevel,
                         receiver,
                         receiver,
                         completionTag);

        (*receiver->rDestroy) (receiver);

        PortalDrop(portal, false);

        if (IsA(parsetree, TransactionStmt))
        {
            /*
             * If this was a transaction control statement, commit it. We will
             * start a new xact command for the next command (if any).
             */
            finish_xact_command();
        }
        else if (lnext(parsetree_item) == NULL)
        {
            /*
             * If this is the last parsetree of the query string, close down
             * transaction statement before reporting command-complete.  This
             * is so that any end-of-transaction errors are reported before
             * the command-complete message is issued, to avoid confusing
             * clients who will expect either a command-complete message or an
             * error, not one and then the other.  But for compatibility with
             * historical Postgres behavior, we do not force a transaction
             * boundary between queries appearing in a single query string.
             */
            finish_xact_command();
        }
        else
        {
            /*
             * We need a CommandCounterIncrement after every query, except
             * those that start or end a transaction block.
             */
            CommandCounterIncrement();
        }

        /*
         * Tell client that we're done with this query.  Note we emit exactly
         * one EndCommand report for each raw parsetree, thus one for each SQL
         * command the client sent, regardless of rewriting. (But a command
         * aborted by error will not send an EndCommand report at all.)
         */
        EndCommand(completionTag, dest);
    }                            /* end loop over parsetrees */




    /*
     * Close down transaction statement, if one is open.
     */
    finish_xact_command();

    /*
     * If there were no parsetrees, return EmptyQueryResponse message.
     */
    if (!parsetree_list)
        NullCommand(dest);

    /*
     * Emit duration logging if appropriate.
     */
    switch (check_log_duration(msec_str, was_logged))
    {
        case 1:
            ereport(LOG,
                    (errmsg("duration: %s ms", msec_str),
                     errhidestmt(true)));
            break;
        case 2:
            ereport(LOG,
                    (errmsg("duration: %s ms  statement: %s",
                            msec_str, query_string),
                     errhidestmt(true),
                     errdetail_execute(parsetree_list)));
            break;
    }

    if (save_log_statement_stats)
        ShowUsage("QUERY STATISTICS");

    TRACE_POSTGRESQL_QUERY_DONE(query_string);

    debug_query_string = NULL;

}

其中，从 portal = CreatePortal("", true, true); 这一句开始，就是准备要执行了。