[YSQL] Upgrade fails for indexes with hash column groups

[pilshchikov]

Jira Link: DB-17218

Description

Im trying to do upgrade 2024.2.4.0-b61 -> 2025.1.0.0-b129 under load and it failed. Then i done retry without load and it also failed
Error:

Server[YB Master - 172.151.20.3:7100] RUNTIME_ERROR[code 7]: Failed to run pg_upgrade: pg_upgrade failed. Check previous errors for more details.: Subprocess '/home/yugabyte/yb-software/yugabyte-2025.1.0.0-b129-almalinux8-aarch64/postgres/bin/pg_upgrade' terminated with non-zero exit status 256.

Steps:

1. Create node 5 nodes, RF=3 2024.2.4.0-b61
2. Create some tables and run transactional and non transactional workloads that load CPU till 80% in max
3. Run upgrade to 2025.1.0.0-b129
4. It failed after some time, notice that it failed when it tried to upgrade last master process

Also click retry in YBA, without any load and it still got me the same error

pg_restore: creating INDEX "public.test_bank_1_10idx_ib_part"
pg_restore: while PROCESSING TOC:
pg_restore: from TOC entry 2999; 1259 16463 INDEX test_bank_1_10idx_ib_part postgres
pg_restore: error: could not execute query: ERROR: syntax error at or near "AS"
LINE 1: ...public"."test_bank_1_1" USING "lsm" (("committed" AS "commit...
                               ^
Command was: CREATE INDEX NONCONCURRENTLY "test_bank_1_10idx_ib_part" ON "public"."test_bank_1_1" USING "lsm" (("committed" AS "committed", "balance") HASH AS "balance", "id" DESC AS "id") INCLUDE ("filler" AS "filler") SPLIT INTO 5 TABLETS WHERE (("id" >= 0) OR ("id" IS NULL));

Logs and all links located in JIRA first comment

Issue Type

kind/bug

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[fizaaluthra]

Only affects upgrades (not an issue for new PG15 clusters).
Upgrades will fail when there's an index with hash column groups, example:
CREATE INDEX ON tbl ((a, b) HASH, c DESC);