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When building BRIN indexes, the brinbuildCallback only advances to the next page range when seeing a tuple that doesn't belong to the current one. This means that the index may end up missing ranges at the end of the table, if those pages do not contain any indexable tuples. We tend not to have completely empty pages at the end of a relation, but this also applies to partial indexes, where the tuples may simply not match the index predicate. This results in inefficient scans using the affected BRIN index - without the summaries, the page ranges have to be read and processed, which consumes I/O and possibly also CPU time. The existing code already added empty ranges for earlier parts of the table, this commit makes sure we add them for the ranges at the end of the table too. Patch by Matthias van de Meent, with review/improvements by me. Author: Matthias van de Meent Reviewed-by: Tomas Vondra Discussion: https://postgr.es/m/CAEze2WiMsPZg%3DxkvSF_jt4%3D69k6K7gz5B8V2wY3gCGZ%2B1BzCbQ%40mail.gmail.com
111 lines
3.6 KiB
Plaintext
111 lines
3.6 KiB
Plaintext
CREATE TABLE test1 (a int, b text);
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INSERT INTO test1 VALUES (1, 'one');
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CREATE INDEX test1_a_idx ON test1 USING brin (a);
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SELECT brin_page_type(get_raw_page('test1_a_idx', 0));
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brin_page_type
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----------------
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meta
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(1 row)
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SELECT brin_page_type(get_raw_page('test1_a_idx', 1));
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brin_page_type
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----------------
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revmap
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(1 row)
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SELECT brin_page_type(get_raw_page('test1_a_idx', 2));
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brin_page_type
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----------------
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regular
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(1 row)
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SELECT * FROM brin_metapage_info(get_raw_page('test1_a_idx', 0));
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magic | version | pagesperrange | lastrevmappage
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------------+---------+---------------+----------------
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0xA8109CFA | 1 | 128 | 1
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(1 row)
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SELECT * FROM brin_metapage_info(get_raw_page('test1_a_idx', 1));
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ERROR: page is not a BRIN page of type "metapage"
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DETAIL: Expected special type 0000f091, got 0000f092.
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SELECT * FROM brin_revmap_data(get_raw_page('test1_a_idx', 0)) LIMIT 5;
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ERROR: page is not a BRIN page of type "revmap"
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DETAIL: Expected special type 0000f092, got 0000f091.
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SELECT * FROM brin_revmap_data(get_raw_page('test1_a_idx', 1)) LIMIT 5;
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pages
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-------
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(2,1)
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(0,0)
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(0,0)
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(0,0)
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(0,0)
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(5 rows)
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SELECT * FROM brin_page_items(get_raw_page('test1_a_idx', 2), 'test1_a_idx')
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ORDER BY blknum, attnum LIMIT 5;
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itemoffset | blknum | attnum | allnulls | hasnulls | placeholder | empty | value
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------------+--------+--------+----------+----------+-------------+-------+----------
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1 | 0 | 1 | f | f | f | f | {1 .. 1}
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(1 row)
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-- Mask DETAIL messages as these are not portable across architectures.
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\set VERBOSITY terse
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-- Failures for non-BRIN index.
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CREATE INDEX test1_a_btree ON test1 (a);
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SELECT brin_page_items(get_raw_page('test1_a_btree', 0), 'test1_a_btree');
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ERROR: "test1_a_btree" is not a BRIN index
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SELECT brin_page_items(get_raw_page('test1_a_btree', 0), 'test1_a_idx');
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ERROR: input page is not a valid BRIN page
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-- Invalid special area size
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SELECT brin_page_type(get_raw_page('test1', 0));
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ERROR: input page is not a valid BRIN page
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SELECT * FROM brin_metapage_info(get_raw_page('test1', 0));
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ERROR: input page is not a valid BRIN page
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SELECT * FROM brin_revmap_data(get_raw_page('test1', 0));
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ERROR: input page is not a valid BRIN page
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\set VERBOSITY default
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-- Tests with all-zero pages.
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SHOW block_size \gset
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SELECT brin_page_type(decode(repeat('00', :block_size), 'hex'));
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brin_page_type
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----------------
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(1 row)
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SELECT brin_page_items(decode(repeat('00', :block_size), 'hex'), 'test1_a_idx');
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brin_page_items
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-----------------
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(0 rows)
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SELECT brin_metapage_info(decode(repeat('00', :block_size), 'hex'));
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brin_metapage_info
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--------------------
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(1 row)
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SELECT brin_revmap_data(decode(repeat('00', :block_size), 'hex'));
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brin_revmap_data
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------------------
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(1 row)
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-- Test that partial indexes have all pages, including empty ones.
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CREATE TABLE test2 (a int);
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INSERT INTO test2 SELECT i FROM generate_series(1,1000) s(i);
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-- No rows match the index predicate, make sure the index has the right number
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-- of ranges (same as number of page ranges).
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CREATE INDEX ON test2 USING brin (a) WITH (pages_per_range=1) WHERE (a IS NULL);
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ANALYZE test2;
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-- Does the index have one summary of the relation?
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SELECT (COUNT(*) = (SELECT relpages FROM pg_class WHERE relname = 'test2')) AS ranges_do_match
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FROM generate_series((SELECT (lastrevmappage + 1) FROM brin_metapage_info(get_raw_page('test2_a_idx', 0))),
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(SELECT (relpages - 1) FROM pg_class WHERE relname = 'test2_a_idx')) AS pages(p),
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LATERAL brin_page_items(get_raw_page('test2_a_idx', p), 'test2_a_idx') AS items;
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ranges_do_match
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-----------------
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t
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(1 row)
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DROP TABLE test1;
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DROP TABLE test2;
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