psql: Add support for pipelines

With \bind, \parse, \bind_named and \close, it is possible to issue
queries from psql using the extended protocol.  However, it was not
possible to send these queries using libpq's pipeline mode.  This
feature has two advantages:
- Testing.  Pipeline tests were only possible with pgbench, using TAP
tests.  It now becomes possible to have more SQL tests that are able to
stress the backend with pipelines and extended queries.  More tests will
be added in a follow-up commit that were discussed on some other
threads.  Some external projects in the community had to implement their
own facility to work around this limitation.
- Emulation of custom workloads, with more control over the actions
taken by a client with libpq APIs.  It is possible to emulate more
workload patterns to bottleneck the backend with the extended query
protocol.

This patch adds six new meta-commands to be able to control pipelines:
* \startpipeline starts a new pipeline.  All extended queries are queued
until the end of the pipeline are reached or a sync request is sent and
processed.
* \endpipeline ends an existing pipeline.  All queued commands are sent
to the server and all responses are processed by psql.
* \syncpipeline queues a synchronisation request, without flushing the
commands to the server, equivalent of PQsendPipelineSync().
* \flush, equivalent of PQflush().
* \flushrequest, equivalent of PQsendFlushRequest()
* \getresults reads the server's results for the queries in a pipeline.
Unsent data is automatically pushed when \getresults is called.  It is
possible to control the number of results read in a single meta-command
execution with an optional parameter, 0 means that all the results
should be read.

Author: Anthonin Bonnefoy <[email protected]>
Reviewed-by: Jelte Fennema-Nio <[email protected]>
Reviewed-by: Kirill Reshke <[email protected]>
Discussion: https://postgr.es/m/CAO6_XqroE7JuMEm1sWz55rp9fAYX2JwmcP_3m_v51vnOFdsLiQ@mail.gmail.com

1 files changed, 7 insertions, 0 deletions

diff --git a/src/bin/psql/help.c b/src/bin/psql/help.c
index da8e1ade5df..714b8619233 100644
--- 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");
 	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");
 	HELP0("  \\watch [[i=]SEC] [c=N] [m=MIN]\n"
 		  "                         execute query every SEC seconds, up to N times,\n"
 		  "                         stop if less than MIN rows are returned\n");