Thread: pgsql: Add try_index_open(), conditional variant of index_open()

Add try_index_open(), conditional variant of index_open()

try_index_open() is able to open an index if its relkind fits, except
that it would return NULL instead of generated an error if the relation
does not exist.  This new routine will be used by an upcoming patch to
make REINDEX on partitioned relations more robust when an index in a
partition tree is dropped.

Extracted from a larger patch by the same author.

Author: Fei Changhong
Discussion: https://postgr.es/m/tencent_6A52106095ACDE55333E3AD33F304C0C3909@qq.com
Backpatch-through: 14

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7ce65c6f7209fcbc73605c914c37c4b2a6406213

Modified Files
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src/backend/access/index/indexam.c | 49 +++++++++++++++++++++++++++++++++-----
src/include/access/genam.h         |  1 +
2 files changed, 44 insertions(+), 6 deletions(-)