Postgres 15

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

CREATE TABLE test (y int, x xml);
INSERT INTO test VALUES (1, '<foo>abc</foo>');
INSERT INTO test VALUES (2, '<bar/>');
SELECT * FROM test;

CREATE TABLE

INSERT 0 1

INSERT 0 1

y
x

1
<foo>abc</foo>

2
<bar/>

SELECT 2

INSERT INTO test VALUES (3, 'bar');
INSERT INTO test VALUES (4, 'bar<foo>abc</foo>');
SELECT *, x IS DOCUMENT is_XML FROM test;

INSERT 0 1

INSERT 0 1

y
x
is_xml

1
<foo>abc</foo>
t

2
<bar/>
t

3
bar
f

4
bar<foo>abc</foo>
f

SELECT 4

INSERT INTO test VALUES (5, '<bar');

ERROR:  invalid XML content
LINE 1: INSERT INTO test VALUES (5, '<bar');
                                    ^
DETAIL:  line 1: Couldn't find end of Start Tag bar line 1
<bar
    ^

INSERT INTO test VALUES (6, '<foo>abc<bar>def</foo></bar>');

ERROR:  invalid XML content
LINE 1: INSERT INTO test VALUES (6, '<foo>abc<bar>def</foo></bar>');
                                    ^
DETAIL:  line 1: Opening and ending tag mismatch: bar line 1 and foo
<foo>abc<bar>def</foo></bar>
                      ^
line 1: Opening and ending tag mismatch: foo line 1 and bar
<foo>abc<bar>def</foo></bar>
                            ^
line 1: chunk is not well balanced
<foo>abc<bar>def</foo></bar>
                            ^