avantgardnerio opened a new issue, #13831:
URL: https://github.com/apache/datafusion/issues/13831
### Describe the bug
When attempting to accumulate large text fields with a `group by`, it was
observed that `group_aggregate_batch()` can OOM despite ostensibly using the
`MemoryPool`.
Query:
```
select truncated_time, count(*) AS cnt
from (
select
truncated_time, k8s_deployment_name, message
from (
SELECT
priorityclass,
timestamp,
date_trunc('day', timestamp) AS truncated_time,
k8s_deployment_name,
message
FROM agg_oom
where priorityclass != 'low'
)
group by truncated_time, k8s_deployment_name, message
) group by truncated_time
```
On 8x ~50MB parquet files where the `message` column can be up to 8192 byte
strings. When profiled, by far it was the largest use of memory:
When logging, we can see it fails while interning
```
converting 3 rows
interning 8192 rows with 1486954 bytes
interned 8192 rows, now I'm 13054176 bytes
resizing to 14103171
resizing to 14103171
reserving 28206342 extra bytes
converting 3 rows
interning 8192 rows with 1350859 bytes
memory allocation of 25690112 bytes failed
Aborted (core dumped)
```
### To Reproduce
1. set up a test with
```
let memory_limit = 125_000_000;
let MEMORY_FRACTION = 1.0;
let rt_config = RuntimeConfig::new()
.with_memory_limit(memory_limit, MEMORY_FRACTION);
```
2.set `ulimit -v 1152000`
3. query some parquet files with long strings
### Expected behavior
`group_aggregate_batch()` doesn't make the assumption:
```
// Here we can ignore `insufficient_capacity_err` because we
will spill later,
// but at least one batch should fit in the memory
```
But instead realizes that adding 1 row to a million doesn't allocate
1,000,001, but rather 2,000,000 when the `Vec` exponentially resizes.
### Additional context
Proposed solution:
Add
```
self.reservation.try_resize(self.reservation.size() * 2)?;
```
Above
```
self.group_values
.intern(group_values, &mut self.current_group_indices)?;
```
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