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Commit0635fe0

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Fix overflow when calculating timestamp distance in BRIN
When calculating distances for timestamp values for BRIN minmax-multiindexes, we need to be careful about overflows for extreme values. Ifthe value overflows into a negative value, the index may be inefficient.The new regression test checks this for the timestamp type by adding atable with enough values to force range compaction/merging. The valuesare close to min/max, which means a risk of overflow.Fixed by converting the int64 values to double first, before calculatingthe distance. This prevents the overflow. We may lose some precision, ofcourse, but that's good enough. In the worst case we build a slightlyless efficient index, but for large distances this won't matter.This only affects minmax-multi indexes on timestamp columns, with rangescontaining values sufficiently distant to cause an overflow. That seemslike a fairly rare case in practice.Backpatch to 14, where minmax-multi indexes were introduced.Reported-by: Ashutosh BapatReviewed-by: Ashutosh Bapat, Dean RasheedBackpatch-through: 14Discussion:https://postgr.es/m/eef0ea8c-4aaa-8d0d-027f-58b1f35dd170@enterprisedb.com
1 parent2bf99b4 commit0635fe0

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3 files changed

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3 files changed

+37
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‎src/backend/access/brin/brin_minmax_multi.c

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Original file line numberDiff line numberDiff line change
@@ -2138,7 +2138,7 @@ brin_minmax_multi_distance_timestamp(PG_FUNCTION_ARGS)
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if (TIMESTAMP_NOT_FINITE(dt1)||TIMESTAMP_NOT_FINITE(dt2))
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PG_RETURN_FLOAT8(0);
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delta=dt2-dt1;
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delta=(float8)dt2- (float8)dt1;
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Assert(delta >=0);
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‎src/test/regress/expected/brin_multi.out

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Original file line numberDiff line numberDiff line change
@@ -466,3 +466,18 @@ EXPLAIN (COSTS OFF) SELECT * FROM brin_test_multi WHERE b = 1;
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Filter: (b = 1)
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(2 rows)
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-- test overflows during CREATE INDEX with extreme timestamp values
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CREATE TABLE brin_timestamp_test(a TIMESTAMPTZ);
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SET datestyle TO iso;
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-- values close to timetamp minimum
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INSERT INTO brin_timestamp_test
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SELECT '4713-01-01 00:00:01 BC'::timestamptz + (i || ' seconds')::interval
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FROM generate_series(1,30) s(i);
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-- values close to timetamp maximum
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INSERT INTO brin_timestamp_test
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SELECT '294276-12-01 00:00:01'::timestamptz + (i || ' seconds')::interval
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FROM generate_series(1,30) s(i);
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CREATE INDEX ON brin_timestamp_test USING brin (a timestamptz_minmax_multi_ops) WITH (pages_per_range=1);
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DROP TABLE brin_timestamp_test;
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RESET enable_seqscan;
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RESET datestyle;

‎src/test/regress/sql/brin_multi.sql

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -421,3 +421,24 @@ VACUUM ANALYZE brin_test_multi;
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EXPLAIN (COSTS OFF)SELECT*FROM brin_test_multiWHERE a=1;
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-- Ensure brin index is not used when values are not correlated
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EXPLAIN (COSTS OFF)SELECT*FROM brin_test_multiWHERE b=1;
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-- test overflows during CREATE INDEX with extreme timestamp values
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CREATETABLEbrin_timestamp_test(aTIMESTAMPTZ);
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SET datestyle TO iso;
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-- values close to timetamp minimum
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INSERT INTO brin_timestamp_test
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SELECT'4713-01-01 00:00:01 BC'::timestamptz+ (i||' seconds')::interval
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FROM generate_series(1,30) s(i);
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-- values close to timetamp maximum
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INSERT INTO brin_timestamp_test
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SELECT'294276-12-01 00:00:01'::timestamptz+ (i||' seconds')::interval
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FROM generate_series(1,30) s(i);
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CREATEINDEXON brin_timestamp_test USING brin (a timestamptz_minmax_multi_ops) WITH (pages_per_range=1);
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DROPTABLE brin_timestamp_test;
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RESET enable_seqscan;
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RESET datestyle;

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