-- from it to cause it to be read back into shared buffers.

SELECT sum(reads) AS io_sum_shared_before_reads

FROM pg_stat_io WHERE io_context = 'normal' AND io_object = 'relation' \gset

-- Do this in a transaction to prevent spurious failures due to concurrent accesses to our newly

-- rewritten table, e.g. by autovacuum.

BEGIN;

ALTER TABLE test_io_shared SET TABLESPACE regress_tblspace;

-- SELECT from the table so that the data is read into shared buffers and

-- io_context 'normal', io_object 'relation' reads are counted.

100

(1 row)

COMMIT;

SELECT pg_stat_force_next_flush();

pg_stat_force_next_flush

--------------------------

SELECTsum(reads)AS io_sum_shared_before_reads

FROM pg_stat_ioWHERE io_context='normal'AND io_object='relation' \gset

BEGIN;

ALTERTABLE test_io_sharedSET TABLESPACE regress_tblspace;

SELECTCOUNT(*)FROM test_io_shared;

COMMIT;

SELECT pg_stat_force_next_flush();

SELECTsum(reads)AS io_sum_shared_after_reads

FROM pg_stat_ioWHERE io_context='normal'AND io_object='relation' \gset