When executing 'SELECT COUNT(*) FROM t', the OpenMLDB service exits directly due to being OOM (Out Of Memory) killed.

**Bug Description**

In a bank customer anti-fraud scenario, the primary table t contains 400 million records with a single replica, and the memory utilization is 52%. After executing SELECT COUNT(*) FROM t, the OpenMLDB service exits. Checking the logs reveals an "oom_kill" event.

The issue is about an OOM kill when running SELECT COUNT(*) on a large table. Start by examining the query execution path for aggregate functions, particularly COUNT(*), in the OpenMLDB codebase. Look at memory management during full table scans and check for any known issues with memory allocation or query planning for large datasets. Review the logs for the oom_kill event details to understand the memory pressure. Testing on a smaller dataset to reproduce the memory growth pattern would be a first step.

Written by the indexing model from the issue text.