To: pgsql-hackers@lists.postgresql.org
From: Platon Pronko <platon7pronko@gmail.com>
Subject: very long record lines in expanded psql output
Message-ID: <f03d38a3-db96-a56e-d1bc-dbbc80bbde4d@gmail.com>
Date: Thu, 5 Aug 2021 13:36:45 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.12.0
MIME-Version: 1.0
Content-Type: multipart/mixed;
 boundary="------------C434E484567DFAA9A14C59C0"
Content-Language: en-US
Archived-At: 
 <https://www.postgresql.org/message-id/f03d38a3-db96-a56e-d1bc-dbbc80bbde4d%40gmail.com>
Precedence: bulk

This is a multi-part message in MIME format.
--------------C434E484567DFAA9A14C59C0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit

In expanded mode psql calculates the width of the longest field in all the output rows,
and prints the header line according to it. This often results in record header wrapping
over several lines (see example below).

This huge record header is printed the same way before each record, even if all the fields
in current record are small and fit into terminal width. This often leads to situations
when record header occupies the entirety of the screen, for all records, even though there are
only a few records with huge fields in a record set.

Maybe we can avoid making the header line longer than terminal width for \pset border 0
and \pset border 1? We already have terminal width calculated. Please see attached a patch
with the proposed implementation.

Example output before the modification, in a terminal with a 100-column width:

$ psql template1 -c "\x on" -c "\pset border 1;" -c "select n, repeat('x', n) as long_column_name from unnest(array[42,210]) as n"
Expanded display is on.
Border style is 1.
─[ RECORD 1 ]────┬──────────────────────────────────────────────────────────────────────────────────
────────────────────────────────────────────────────────────────────────────────────────────────────
─────────────────────────────
n                │ 42
long_column_name │ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
─[ RECORD 2 ]────┼──────────────────────────────────────────────────────────────────────────────────
────────────────────────────────────────────────────────────────────────────────────────────────────
─────────────────────────────
n                │ 210
long_column_name │ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx

And here's the same command after the patch:

$ psql template1 -c "\x on" -c "\pset border 1;" -c "select n, repeat('x', n) as long_column_name from unnest(array[42,210]) as n"
Expanded display is on.
Border style is 1.
─[ RECORD 1 ]────┬──────────────────────────────────────────────────────────────────────────────────
n                │ 42
long_column_name │ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
─[ RECORD 2 ]────┼──────────────────────────────────────────────────────────────────────────────────
n                │ 210
long_column_name │ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Best regards,
Platon Pronko

--------------C434E484567DFAA9A14C59C0
Content-Type: text/x-patch; charset=UTF-8;
 name="fix-header-lines-in-expanded-output.patch"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
 filename="fix-header-lines-in-expanded-output.patch"

diff --git a/src/fe_utils/print.c b/src/fe_utils/print.c
index d48fcc4a03..9483d0d852 100644
--- a/src/fe_utils/print.c
+++ b/src/fe_utils/print.c
@@ -1157,6 +1157,7 @@ print_aligned_vertical_line(const printTextFormat *format,
 							unsigned long record,
 							unsigned int hwidth,
 							unsigned int dwidth,
+							int output_columns,
 							printTextRule pos,
 							FILE *fout)
 {
@@ -1200,6 +1201,14 @@ print_aligned_vertical_line(const printTextFormat *format,
 	}
 	if (reclen < 0)
 		reclen = 0;
+
+	if (output_columns > 0) {
+		if (opt_border == 0)
+			dwidth = Min(dwidth, output_columns - hwidth);
+		if (opt_border == 1)
+			dwidth = Min(dwidth, output_columns - hwidth - 3);
+	}
+
 	for (i = reclen; i < dwidth; i++)
 		fputs(opt_border > 0 ? lformat->hrule : " ", fout);
 	if (opt_border == 2)
@@ -1501,10 +1510,11 @@ print_aligned_vertical(const printTableContent *cont,
 
 			if (!opt_tuples_only)
 				print_aligned_vertical_line(format, opt_border, record++,
-											lhwidth, dwidth, pos, fout);
+											lhwidth, dwidth, output_columns,
+											pos, fout);
 			else if (i != 0 || !cont->opt->start_table || opt_border == 2)
 				print_aligned_vertical_line(format, opt_border, 0, lhwidth,
-											dwidth, pos, fout);
+											dwidth, output_columns, pos, fout);
 		}
 
 		/* Format the header */
@@ -1691,7 +1701,7 @@ print_aligned_vertical(const printTableContent *cont,
 	{
 		if (opt_border == 2 && !cancel_pressed)
 			print_aligned_vertical_line(format, opt_border, 0, hwidth, dwidth,
-										PRINT_RULE_BOTTOM, fout);
+										output_columns, PRINT_RULE_BOTTOM, fout);
 
 		/* print footers */
 		if (!opt_tuples_only && cont->footers != NULL && !cancel_pressed)

--------------C434E484567DFAA9A14C59C0--