Support multiple statements

[Hydrocharged]

This allows for handling multiple statements within a single Query message. This fixes:

• Error: only a single statement at a time is currently supported (transaction support?) #2175

This also tests the contents of the messages returned, which were verified using Wireshark on a local Postgres instance as the source-of-truth.

[github-actions]

	Main	PR
covering_index_scan_postgres	544.39/s	547.32/s	+0.5%
index_join_postgres	125.87/s	127.24/s	+1.0%
index_join_scan_postgres	184.42/s	186.40/s	+1.0%
index_scan_postgres	11.21/s	11.37/s	+1.4%
oltp_point_select	2244.34/s	2415.55/s	+7.6%
oltp_read_only	1689.13/s	1745.71/s	+3.3%
select_random_points	110.34/s	112.57/s	+2.0%
select_random_ranges	435.66/s	438.86/s	+0.7%
table_scan_postgres	11.18/s	11.23/s	+0.4%
types_table_scan_postgres	5.16/s	5.18/s	+0.3%

[github-actions]

	Main	PR
Total	42090	42090
Successful	17559	17563
Failures	24531	24527
Partial Successes1	5584	5582

	Main	PR
Successful	41.7177%	41.7273%
Failures	58.2823%	58.2727%

${\color{red}Regressions (1)}$

copyselect

QUERY:          drop table test3;
RECEIVED ERROR: COPY DATA message received without a COPY FROM STDIN operation in progress

${\color{lightgreen}Progressions (13)}$

copyselect

QUERY: select 0; copy test3 from stdin; copy test3 from stdin; select 1;

psql

QUERY: CREATE TABLE foo(s TEXT) ;
ROLLBACK;

QUERY: DROP TABLE foo ;
ROLLBACK;

QUERY: BEGIN ;
CREATE TABLE foo(s TEXT) ;
INSERT INTO foo(s) VALUES ('hello'), ('world') ;
COMMIT;

QUERY: SELECT COUNT(*) AS "#mum"
FROM bla WHERE s = 'Mum' ;               -- no mum here
SELECT * FROM bla ORDER BY 1;

transactions

QUERY: SELECT 1; SELECT 2; SELECT 3;

QUERY: insert into i_table values(1); select * from i_table;

QUERY: begin; insert into i_table values(3); commit;

QUERY: begin; insert into i_table values(4); rollback;

QUERY: select 1; begin; insert into i_table values(5);

QUERY: select 1; begin; insert into i_table values(6);

QUERY: insert into i_table values(9); rollback; select 2;

QUERY: SELECT 1; BEGIN; SAVEPOINT sp; ROLLBACK TO SAVEPOINT sp; COMMIT;

Footnotes

1. These are tests that we're marking as Successful, however they do not match the expected output in some way. This is due to small differences, such as different wording on the error messages, or the column names being incorrect while the data itself is correct. ↩

[zachmu]

LGTM but see comment about handling of empty queries in batches