Use SYNC_REPLICATION_MODE, NUM_SYNC_REPLICAS, SYNC_COMMIT_LEVEL in sync scripts (v9–v18)

[souravbiswassanto]

Summary

Extends the synchronous replication block in all 40 role scripts (v9–v18) to use SYNC_STANDBY_NAMES when set, falling back to the existing auto-generation loop when not.

Logic (all scripts: primary/start.sh, standby/run.sh, standby/warm_stanby.sh, standby/ha_backup_job.sh)

if [[ -n "${SYNC_STANDBY_NAMES:-}" ]]; then
    # Use explicit ordered list from operator
    IFS=',' read -ra _standby_list <<< "$SYNC_STANDBY_NAMES"
    for _name in "${_standby_list[@]}"; do
        names+="\"${_name}\","
    done
    names="${names%,}"
else
    # Auto-generate from pod index (existing behaviour)
    self_idx=${HOSTNAME##*[!0-9]}
    ...
fi
echo "synchronous_standby_names = '${SYNC_REPLICATION_MODE:-ANY} ${NUM_SYNC_REPLICAS:-1} ("$names")'"

What this unlocks

• Priority ordering (mode: First): FIRST 1 ("postgres-2","postgres-0") — explicit preference
• Selective exclusion: omit cross-region standbys from the sync set

What is NOT changed

remote-replica.sh files — those use '*' (all standbys), unrelated to this feature.

Backwards compatibility

Shell :- defaults on all three env vars mean scripts behave identically when running against an older operator that doesn't set these vars.

Dependency

https://github.com/kubedb/postgres/pull/904 (operator) / kubedb/apimachinery#1782 (API)

Test plan

• All 10 versions tested with no env vars — behaviour unchanged
• SYNC_STANDBY_NAMES=postgres-2,postgres-0 SYNC_REPLICATION_MODE=FIRST NUM_SYNC_REPLICAS=1 — verify synchronous_standby_names = 'FIRST 1 ("postgres-2","postgres-0")'
• Verify 0 remote-replica.sh files touched

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