btree_gin: Fix timestamp-vs-timestamptz comparisons near DST boundary. To perform cross-type index scans with a timestamp index and a timestamptz comparison value, btree_gin must convert the timestamptz to timestamp to establish the starting point for the indexscan. This is hazardous because timestamp_cmp_timestamptz is actually defined to upconvert the timestamp to timestamptz and then compare timestamptz's. When dealing with ambiguous timestamps near a fall-back DST transition, the value may not round-trip, leading to selecting a scan start point that misses some index entries that should match.
To fix that, move the converted value back an hour at a time until it's clearly <= the given comparison value. (We could try to be smarter, but this way seems more certain to work across all possible DST behaviors.) Another hazard is that for timestamptz's that are finite but close to the upper range limit, the conversion may produce timestamp +Infinity, again comparing greater than the given value. It's less clear whether this can lead to missing matching values in practice, but it would at least risk making the aforesaid correction loop very slow. So replace +Infinity by the maximum finite timestamp. The reverse case of timestamptz index and timestamp comparison value is not at risk because upconverting the timestamp stays consistent with what timestamptz_cmp_timestamp will do. Also, while date-vs-timestamptz could theoretically be at risk, the conversion error would have to be a full day which seems not to occur in reality. Author: shihao zhong <[email protected]> Reviewed-by: Tom Lane <[email protected]> Discussion: https://postgr.es/m/CAGRkXqQio=7pwgtfkvjyqy9-7a_0a36e3put1gxjedypgqf...@mail.gmail.com Backpatch-through: 19 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/aadce2c10ffec9326a5119a3c590b77ab58b4f97 Modified Files -------------- contrib/btree_gin/btree_gin.c | 28 ++++++++++++++++++++++++++++ contrib/btree_gin/expected/timestamp.out | 26 ++++++++++++++++++++++++++ contrib/btree_gin/sql/timestamp.sql | 9 +++++++++ 3 files changed, 63 insertions(+)
