pipelining in psql, commit 41625ab

On Fri, Feb 21, 2025 at 11:33:41AM +0900, Michael Paquier wrote:
> So let's take one step here, I have applied the main patch.

commit 41625ab wrote:
>     * \syncpipeline queues a synchronisation request, without flushing the
>     commands to the server, equivalent of PQsendPipelineSync().

libpq has both PQpipelineSync() and PQsendPipelineSync(), so I find it odd
that the psql command for PQsendPipelineSync() is \syncpipeline.  I would have
expected the word "send" somewhere in its name.  That said, maybe having
PQpipelineSync() was a mistake, since I think it's just PQsendPipelineSync() +
PQflush().  In that light, it's reasonable not to spread the extra "send" word
into psql.  \syncpipeline is fine with me, but it's worth others taking a
second look.

> +				pg_log_error("\\getresults: invalid number of requested results");
> +				return PSQL_CMD_SKIP_LINE;

This should be PSQL_CMD_ERROR.  That matters under ON_ERROR_STOP=1.

> --- a/src/bin/psql/help.c
> +++ b/src/bin/psql/help.c
> @@ -167,15 +167,22 @@ slashUsage(unsigned short int pager)
>  	HELP0("  \\close STMT_NAME       close an existing prepared statement\n");
>  	HELP0("  \\copyright             show PostgreSQL usage and distribution terms\n");
>  	HELP0("  \\crosstabview [COLUMNS] execute query and display result in crosstab\n");
> +	HELP0("  \\endpipeline           exit pipeline mode\n");
>  	HELP0("  \\errverbose            show most recent error message at maximum verbosity\n");
> +	HELP0("  \\flush                 push unsent data to the server\n");
> +	HELP0("  \\flushrequest          send a flushrequest command\n");

protocol.sgml calls it a "Flush command".

>  	HELP0("  \\g [(OPTIONS)] [FILE]  execute query (and send result to file or |pipe);\n"
>  		  "                         \\g with no arguments is equivalent to a semicolon\n");
>  	HELP0("  \\gdesc                 describe result of query, without executing it\n");
> +	HELP0("  \\getresults [NUM_RES]  read NUM_RES pending results. All pending results are\n"
> +		  "                         read if no argument is provided\n");
>  	HELP0("  \\gexec                 execute query, then execute each value in its result\n");
>  	HELP0("  \\gset [PREFIX]         execute query and store result in psql variables\n");
>  	HELP0("  \\gx [(OPTIONS)] [FILE] as \\g, but forces expanded output mode\n");
>  	HELP0("  \\parse STMT_NAME       create a prepared statement\n");
>  	HELP0("  \\q                     quit psql\n");
> +	HELP0("  \\startpipeline         enter pipeline mode\n");
> +	HELP0("  \\syncpipeline          add a synchronisation point to an ongoing pipeline\n");

v17 "\?" has a 14-line "General" section:

General
  \bind [PARAM]...       set query parameters
  \copyright             show PostgreSQL usage and distribution terms
  \crosstabview [COLUMNS] execute query and display result in crosstab
  \errverbose            show most recent error message at maximum verbosity
  \g [(OPTIONS)] [FILE]  execute query (and send result to file or |pipe);
                         \g with no arguments is equivalent to a semicolon
  \gdesc                 describe result of query, without executing it
  \gexec                 execute query, then execute each value in its result
  \gset [PREFIX]         execute query and store result in psql variables
  \gx [(OPTIONS)] [FILE] as \g, but forces expanded output mode
  \q                     quit psql
  \watch [[i=]SEC] [c=N] [m=MIN]
                         execute query every SEC seconds, up to N times,
                         stop if less than MIN rows are returned

v18 has raised that to 26 lines via $SUBJECT and other additions.  I think a
new "Extended Query Protocol" section should house \bind and all the v18
additions.  Beginners should ignore the new section.  The section may as well
appear last.  What do you think?