Associative array ordering in awk during migration

Goal

Replace a legacy script that reads a log file, counts occurrences per user, and writes a sorted report. The replacement must run with the existing cron job and produce identical output without downtime.

Constraints

The new script must use a single awk invocation, as the environment only provides the default awk binary (POSIX). The log file is large, so memory usage must be bounded. The report must list users in ascending order of their IDs.

Unresolved Decision

Associative arrays in awk do not guarantee key order. This raises uncertainty about whether the report will be sorted correctly.

Questions

• Does the default awk implementation maintain insertion order for associative array keys when iterating with for (k in a)?
• Is there a portable way to produce a sorted list of keys without invoking external utilities like sort?
• Do any awk extensions or flags (e.g., --posix, --non-decimal-data) affect key ordering behavior?