From f347ec76e2a227e5c5b5065cce7adad16d58d209 Mon Sep 17 00:00:00 2001 From: Daniel Gustafsson Date: Tue, 29 Aug 2023 11:30:11 +0200 Subject: [PATCH] Allow \watch queries to stop on minimum rows returned When running a repeat query with \watch in psql, it can be helpful to be able to stop the watch process when the query no longer returns the expected amount of rows. An example would be to watch for the presence of a certain event in pg_stat_activity and stopping when the event is no longer present, or to watch an index creation and stop when the index is created. This adds a min_rows=MIN parameter to \watch which can be set to a non-negative integer, and the watch query will stop executing when it returns less than MIN rows. Author: Greg Sabino Mullane Reviewed-by: Michael Paquier Reviewed-by: Daniel Gustafsson Discussion: https://postgr.es/m/CAKAnmmKStATuddYxP71L+p0DHtp9Rvjze3XRoy0Dyw67VQ45UA@mail.gmail.com --- doc/src/sgml/ref/psql-ref.sgml | 7 ++++--- src/bin/psql/command.c | 32 +++++++++++++++++++++++++++----- src/bin/psql/common.c | 19 ++++++++++++++----- src/bin/psql/common.h | 2 +- src/bin/psql/help.c | 4 +++- src/bin/psql/t/001_basic.pl | 23 +++++++++++++++++++++++ 6 files changed, 72 insertions(+), 15 deletions(-) diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml index 182e58353f1..d94e3cacfcc 100644 --- a/doc/src/sgml/ref/psql-ref.sgml +++ b/doc/src/sgml/ref/psql-ref.sgml @@ -3566,13 +3566,14 @@ testdb=> \setenv LESS -imx4F - \watch [ i[nterval]=seconds ] [ c[ount]=times ] [ seconds ] + \watch [ i[nterval]=seconds ] [ c[ount]=times ] [ m[in_rows]=rows ] [ seconds ] Repeatedly execute the current query buffer (as \g does) until interrupted, or the query fails, or the execution count limit - (if given) is reached. Wait the specified number of - seconds (default 2) between executions. For backwards compatibility, + (if given) is reached, or the query no longer returns the minimum number + of rows. Wait the specified number of seconds (default 2) between executions. + For backwards compatibility, seconds can be specified with or without an interval= prefix. Each query result is diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c index 1300869d797..bcd8eb35387 100644 --- a/src/bin/psql/command.c +++ b/src/bin/psql/command.c @@ -162,7 +162,7 @@ static bool do_connect(enum trivalue reuse_previous_specification, static bool do_edit(const char *filename_arg, PQExpBuffer query_buf, int lineno, bool discard_on_quit, bool *edited); static bool do_shell(const char *command); -static bool do_watch(PQExpBuffer query_buf, double sleep, int iter); +static bool do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows); static bool lookup_object_oid(EditableObjectType obj_type, const char *desc, Oid *obj_oid); static bool get_create_object_cmd(EditableObjectType obj_type, Oid oid, @@ -2775,13 +2775,15 @@ exec_command_watch(PsqlScanState scan_state, bool active_branch, { bool have_sleep = false; bool have_iter = false; + bool have_min_rows = false; double sleep = 2; int iter = 0; + int min_rows = 0; /* * Parse arguments. We allow either an unlabeled interval or * "name=value", where name is from the set ('i', 'interval', 'c', - * 'count'). + * 'count', 'm', 'min_rows'). */ while (success) { @@ -2838,6 +2840,26 @@ exec_command_watch(PsqlScanState scan_state, bool active_branch, } } } + else if (strncmp("m=", opt, strlen("m=")) == 0 || + strncmp("min_rows=", opt, strlen("min_rows=")) == 0) + { + if (have_min_rows) + { + pg_log_error("\\watch: minimum row count specified more than once"); + success = false; + } + else + { + have_min_rows = true; + errno = 0; + min_rows = strtoint(valptr, &opt_end, 10); + if (min_rows <= 0 || *opt_end || errno == ERANGE) + { + pg_log_error("\\watch: incorrect minimum row count \"%s\"", valptr); + success = false; + } + } + } else { pg_log_error("\\watch: unrecognized parameter \"%s\"", opt); @@ -2874,7 +2896,7 @@ exec_command_watch(PsqlScanState scan_state, bool active_branch, /* If query_buf is empty, recall and execute previous query */ (void) copy_previous_query(query_buf, previous_buf); - success = do_watch(query_buf, sleep, iter); + success = do_watch(query_buf, sleep, iter, min_rows); } /* Reset the query buffer as though for \r */ @@ -5144,7 +5166,7 @@ do_shell(const char *command) * onto a bunch of exec_command's variables to silence stupider compilers. */ static bool -do_watch(PQExpBuffer query_buf, double sleep, int iter) +do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows) { long sleep_ms = (long) (sleep * 1000); printQueryOpt myopt = pset.popt; @@ -5274,7 +5296,7 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter) myopt.title = title; /* Run the query and print out the result */ - res = PSQLexecWatch(query_buf->data, &myopt, pagerpipe); + res = PSQLexecWatch(query_buf->data, &myopt, pagerpipe, min_rows); /* * PSQLexecWatch handles the case where we can no longer repeat the diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c index 10ad1f2538d..ede197bebeb 100644 --- a/src/bin/psql/common.c +++ b/src/bin/psql/common.c @@ -36,6 +36,7 @@ static int ExecQueryAndProcessResults(const char *query, double *elapsed_msec, bool *svpt_gone_p, bool is_watch, + int min_rows, const printQueryOpt *opt, FILE *printQueryFout); static bool command_no_begin(const char *query); @@ -632,7 +633,7 @@ PSQLexec(const char *query) * e.g., because of the interrupt, -1 on error. */ int -PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout) +PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout, int min_rows) { bool timing = pset.timing; double elapsed_msec = 0; @@ -646,7 +647,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout) SetCancelConn(pset.db); - res = ExecQueryAndProcessResults(query, &elapsed_msec, NULL, true, opt, printQueryFout); + res = ExecQueryAndProcessResults(query, &elapsed_msec, NULL, true, min_rows, opt, printQueryFout); ResetCancelConn(); @@ -1134,7 +1135,7 @@ SendQuery(const char *query) pset.crosstab_flag || !is_select_command(query)) { /* Default fetch-it-all-and-print mode */ - OK = (ExecQueryAndProcessResults(query, &elapsed_msec, &svpt_gone, false, NULL, NULL) > 0); + OK = (ExecQueryAndProcessResults(query, &elapsed_msec, &svpt_gone, false, 0, NULL, NULL) > 0); } else { @@ -1415,11 +1416,12 @@ DescribeQuery(const char *query, double *elapsed_msec) static int ExecQueryAndProcessResults(const char *query, double *elapsed_msec, bool *svpt_gone_p, - bool is_watch, + bool is_watch, int min_rows, const printQueryOpt *opt, FILE *printQueryFout) { bool timing = pset.timing; bool success; + bool return_early = false; instr_time before, after; PGresult *result; @@ -1461,6 +1463,10 @@ ExecQueryAndProcessResults(const char *query, /* first result */ result = PQgetResult(pset.db); + if (min_rows > 0 && PQntuples(result) < min_rows) + { + return_early = true; + } while (result != NULL) { @@ -1683,7 +1689,10 @@ ExecQueryAndProcessResults(const char *query, if (!CheckConnection()) return -1; - return cancel_pressed ? 0 : success ? 1 : -1; + if (cancel_pressed || return_early) + return 0; + + return success ? 1 : -1; } diff --git a/src/bin/psql/common.h b/src/bin/psql/common.h index 812b94a9775..a16c56b405b 100644 --- a/src/bin/psql/common.h +++ b/src/bin/psql/common.h @@ -32,7 +32,7 @@ extern void psql_setup_cancel_handler(void); extern void SetShellResultVariables(int wait_result); extern PGresult *PSQLexec(const char *query); -extern int PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout); +extern int PSQLexecWatch(const char *query, const printQueryOpt *opt, FILE *printQueryFout, int min_rows); extern bool SendQuery(const char *query); diff --git a/src/bin/psql/help.c b/src/bin/psql/help.c index b2b749d69a5..38c165a6270 100644 --- a/src/bin/psql/help.c +++ b/src/bin/psql/help.c @@ -200,7 +200,9 @@ slashUsage(unsigned short int pager) 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(" \\q quit psql\n"); - HELP0(" \\watch [[i=]SEC] [c=N] execute query every SEC seconds, up to N times\n"); + HELP0(" \\watch [[i=]SEC] [c=N] [m=MIN]\n"); + HELP0(" execute query every SEC seconds, up to N times\n"); + HELP0(" stop if less than MIN rows are returned\n"); HELP0("\n"); HELP0("Help\n"); diff --git a/src/bin/psql/t/001_basic.pl b/src/bin/psql/t/001_basic.pl index 9ac27db2120..5398a1dbf3d 100644 --- a/src/bin/psql/t/001_basic.pl +++ b/src/bin/psql/t/001_basic.pl @@ -355,6 +355,29 @@ psql_like( psql_like($node, sprintf('SELECT 1 \watch c=3 i=%g', 0.01), qr/1\n1\n1/, '\watch with 3 iterations'); +# Check \watch minimum row count +psql_fails_like( + $node, + 'SELECT 3 \watch m=x', + qr/incorrect minimum row count/, + '\watch, invalid minimum row setting'); + +psql_fails_like( + $node, + 'SELECT 3 \watch m=1 min_rows=2', + qr/minimum row count specified more than once/, + '\watch, minimum rows is specified more than once'); + +psql_like( + $node, + q{with x as ( + select now()-backend_start AS howlong + from pg_stat_activity + where pid = pg_backend_pid() + ) select 123 from x where howlong < '2 seconds' \watch i=0.5 m=2}, + qr/^123$/, + '\watch, 2 minimum rows'); + # Check \watch errors psql_fails_like( $node, -- 2.30.2