[outputs.postgresql] Telegraf internal error counters are not incremented when errors occur in postgresql output plugin

Nobody has claimed this yet.

### Relevant telegraf.conf

```toml
[agent]
debug = true
interval = "10s" # default
flush_interval = "10s" # default
round_interval = true # default

[[inputs.internal]]
collect_memstats = true
per_instance = false # default
collect_gostats = false # default

[[inputs.exec]]
commands = [
'''bash -lc 'cat << "EOF"
measurements,device_id=dev1 metric_name="a",metric_value=1.0 1758804689000000000
measurements,device_id=dev1 metric_name="b",metric_value=2.0 1758804690000000000
measurements,device_id=dev1 metric_name="c",metric_value=3.0 1758804691000000000
EOF' '''
]
data_format = "influx"

[[outputs.file]]
files = ["stdout"]

[[outputs.postgresql]]
namepass = ["measurements"]
tagexclude = ["host"]
connection = "host=postgres user=ingester password=ingester_password dbname=pgdb sslmode=disable"
schema = "core"
timestamp_column_name = "observed_at"
timestamp_column_type = "timestamp with time zone"
create_templates = []
add_column_templates = []
```

### Logs from Telegraf

```text
telegraf-1 | 2025-09-25T14:29:48.002754157Z internal_parser,host=978ec7e2d72e,type=influx,version=1.36.1 metrics_parsed=0i,parse_time_ns=0i,errors=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.002900615Z internal_write,host=978ec7e2d72e,input=exec,version=1.36.1 startup_errors=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.002928107Z internal_write,host=978ec7e2d72e,input=internal,version=1.36.1 startup_errors=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003253390Z internal_gather,host=978ec7e2d72e,input=exec,version=1.36.1 errors=0i,metrics_gathered=0i,gather_time_ns=0i,gather_timeouts=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003292504Z internal_write,host=978ec7e2d72e,output=file,version=1.36.1 buffer_limit=10000i,startup_errors=0i,errors=0i,metrics_added=0i,metrics_filtered=0i,buffer_size=0i,write_time_ns=0i,metrics_written=0i,metrics_rejected=0i,metrics_dropped=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003310916Z internal_agent,go_version=1.25.1,host=978ec7e2d72e,version=1.36.1 metrics_dropped=0i,metrics_gathered=0i,gather_errors=0i,gather_timeouts=0i,metrics_written=0i,metrics_rejected=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003325078Z internal_serializer,host=978ec7e2d72e,type=influx,version=1.36.1 serialization_time_ns=0i,errors=0i,metrics_serialized=0i,bytes_serialized=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003346614Z internal_gather,host=978ec7e2d72e,input=internal,version=1.36.1 errors=0i,metrics_gathered=0i,gather_time_ns=0i,gather_timeouts=0i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003389560Z internal_write,host=978ec7e2d72e,output=postgresql,version=1.36.1 metrics_filtered=0i,errors=0i,metrics_dropped=0i,buffer_size=0i,write_time_ns=0i,startup_errors=0i,metrics_added=0i,metrics_written=0i,metrics_rejected=0i,buffer_limit=10000i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.003400390Z internal_memstats,host=978ec7e2d72e sys_bytes=27966371i,pointer_lookups=0i,mallocs=119514i,heap_sys_bytes=20152320i,heap_released_bytes=3080192i,heap_objects=69217i,frees=50297i,heap_alloc_bytes=14834296i,heap_idle_bytes=3137536i,heap_in_use_bytes=17014784i,num_gc=2i,alloc_bytes=14834296i,total_alloc_bytes=21300928i 1758810580000000000
telegraf-1 | 2025-09-25T14:29:48.004532527Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="a",metric_value=1 1758804689000000000
telegraf-1 | 2025-09-25T14:29:48.005300185Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="b",metric_value=2 1758804690000000000
telegraf-1 | 2025-09-25T14:29:48.005321137Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="c",metric_value=3 1758804691000000000
telegraf-1 | 2025-09-25T14:29:48.005404197Z 2025-09-25T14:29:48Z D! [outputs.file] Wrote batch of 13 metrics in 6.72655ms
telegraf-1 | 2025-09-25T14:29:48.005874188Z 2025-09-25T14:29:48Z D! [outputs.file] Buffer fullness: 0 / 10000 metrics
telegraf-1 | 2025-09-25T14:29:48.075825595Z 2025-09-25T14:29:48Z E! [outputs.postgresql] write error (permanent, dropping sub-batch): metric/table mismatch: Unable to omit field/column from "measurements": critical column "observed_at"
telegraf-1 | 2025-09-25T14:29:48.076803026Z 2025-09-25T14:29:48Z D! [outputs.postgresql] Wrote batch of 3 metrics in 78.744912ms
telegraf-1 | 2025-09-25T14:29:48.076868590Z 2025-09-25T14:29:48Z D! [outputs.postgresql] Buffer fullness: 0 / 10000 metrics
telegraf-1 | 2025-09-25T14:29:57.998786228Z internal_gather,host=978ec7e2d72e,input=internal,version=1.36.1 gather_timeouts=0i,errors=0i,metrics_gathered=10i,gather_time_ns=11526272i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.998903570Z internal_write,host=978ec7e2d72e,input=internal,version=1.36.1 startup_errors=0i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.998931729Z internal_gather,host=978ec7e2d72e,input=exec,version=1.36.1 errors=0i,metrics_gathered=3i,gather_time_ns=90523695i,gather_timeouts=0i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.998875162Z 2025-09-25T14:29:57Z D! [outputs.file] Wrote batch of 13 metrics in 378.475µs
telegraf-1 | 2025-09-25T14:29:57.999065274Z 2025-09-25T14:29:57Z D! [outputs.file] Buffer fullness: 0 / 10000 metrics
telegraf-1 | 2025-09-25T14:29:57.998989962Z internal_write,host=978ec7e2d72e,output=file,version=1.36.1 startup_errors=0i,errors=0i,metrics_rejected=0i,metrics_dropped=0i,metrics_added=13i,metrics_written=13i,buffer_limit=10000i,metrics_filtered=0i,buffer_size=0i,write_time_ns=6726550i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999117718Z internal_write,host=978ec7e2d72e,output=postgresql,version=1.36.1 buffer_limit=10000i,metrics_filtered=10i,startup_errors=0i,metrics_added=3i,metrics_written=3i,metrics_rejected=0i,buffer_size=0i,errors=0i,write_time_ns=78744912i,metrics_dropped=0i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999164829Z internal_agent,go_version=1.25.1,host=978ec7e2d72e,version=1.36.1 gather_errors=0i,gather_timeouts=0i,metrics_written=16i,metrics_rejected=0i,metrics_dropped=0i,metrics_gathered=13i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999202694Z internal_parser,host=978ec7e2d72e,type=influx,version=1.36.1 metrics_parsed=3i,parse_time_ns=2404318i,errors=0i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999269758Z internal_serializer,host=978ec7e2d72e,type=influx,version=1.36.1 errors=0i,metrics_serialized=13i,bytes_serialized=2129i,serialization_time_ns=4771231i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999280963Z internal_write,host=978ec7e2d72e,input=exec,version=1.36.1 startup_errors=0i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999289836Z internal_memstats,host=978ec7e2d72e alloc_bytes=14919296i,total_alloc_bytes=21385928i,mallocs=120519i,frees=50329i,heap_sys_bytes=20119552i,heap_in_use_bytes=17047552i,heap_objects=70190i,sys_bytes=27966371i,pointer_lookups=0i,heap_alloc_bytes=14919296i,heap_idle_bytes=3072000i,heap_released_bytes=3014656i,num_gc=2i 1758810590000000000
telegraf-1 | 2025-09-25T14:29:57.999299333Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="a",metric_value=1 1758804689000000000
telegraf-1 | 2025-09-25T14:29:57.999311621Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="b",metric_value=2 1758804690000000000
telegraf-1 | 2025-09-25T14:29:57.999320035Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="c",metric_value=3 1758804691000000000
telegraf-1 | 2025-09-25T14:29:58.006981362Z 2025-09-25T14:29:58Z E! [outputs.postgresql] write error (permanent, dropping sub-batch): metric/table mismatch: Unable to omit field/column from "measurements": critical column "observed_at"
telegraf-1 | 2025-09-25T14:29:58.007252535Z 2025-09-25T14:29:58Z D! [outputs.postgresql] Wrote batch of 3 metrics in 8.667249ms
telegraf-1 | 2025-09-25T14:29:58.007285026Z 2025-09-25T14:29:58Z D! [outputs.postgresql] Buffer fullness: 0 / 10000 metrics
telegraf-1 | 2025-09-25T14:30:08.003302535Z internal_write,host=978ec7e2d72e,output=postgresql,version=1.36.1 metrics_written=6i,metrics_rejected=0i,metrics_dropped=0i,buffer_size=0i,metrics_filtered=20i,errors=0i,write_time_ns=8667249i,metrics_added=6i,buffer_limit=10000i,startup_errors=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003759571Z internal_agent,go_version=1.25.1,host=978ec7e2d72e,version=1.36.1 metrics_dropped=0i,metrics_gathered=26i,gather_errors=0i,gather_timeouts=0i,metrics_written=32i,metrics_rejected=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003801988Z internal_write,host=978ec7e2d72e,input=exec,version=1.36.1 startup_errors=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003825029Z internal_serializer,host=978ec7e2d72e,type=influx,version=1.36.1 serialization_time_ns=5038196i,errors=0i,metrics_serialized=26i,bytes_serialized=4307i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003843404Z internal_gather,host=978ec7e2d72e,input=internal,version=1.36.1 metrics_gathered=20i,gather_time_ns=1978272i,gather_timeouts=0i,errors=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003862654Z internal_write,host=978ec7e2d72e,input=internal,version=1.36.1 startup_errors=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003882445Z internal_gather,host=978ec7e2d72e,input=exec,version=1.36.1 gather_time_ns=83936439i,gather_timeouts=0i,errors=0i,metrics_gathered=6i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003904653Z internal_write,host=978ec7e2d72e,output=file,version=1.36.1 write_time_ns=378475i,startup_errors=0i,metrics_dropped=0i,buffer_size=0i,errors=0i,metrics_added=26i,metrics_written=26i,metrics_rejected=0i,buffer_limit=10000i,metrics_filtered=0i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003977652Z internal_parser,host=978ec7e2d72e,type=influx,version=1.36.1 errors=0i,metrics_parsed=6i,parse_time_ns=2443223i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.003683739Z 2025-09-25T14:30:08Z D! [outputs.file] Wrote batch of 13 metrics in 848.615µs
telegraf-1 | 2025-09-25T14:30:08.004128025Z 2025-09-25T14:30:08Z D! [outputs.file] Buffer fullness: 0 / 10000 metrics
telegraf-1 | 2025-09-25T14:30:08.004037485Z internal_memstats,host=978ec7e2d72e total_alloc_bytes=21456624i,pointer_lookups=0i,heap_sys_bytes=20152320i,heap_idle_bytes=3055616i,heap_in_use_bytes=17096704i,heap_objects=70897i,sys_bytes=27966371i,mallocs=121256i,frees=50359i,heap_alloc_bytes=14989992i,heap_released_bytes=2981888i,num_gc=2i,alloc_bytes=14989992i 1758810600000000000
telegraf-1 | 2025-09-25T14:30:08.004645644Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="a",metric_value=1 1758804689000000000
telegraf-1 | 2025-09-25T14:30:08.004771018Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="b",metric_value=2 1758804690000000000
telegraf-1 | 2025-09-25T14:30:08.004797226Z measurements,device_id=dev1,host=978ec7e2d72e metric_name="c",metric_value=3 1758804691000000000
telegraf-1 | 2025-09-25T14:30:08.010702531Z 2025-09-25T14:30:08Z E! [outputs.postgresql] write error (permanent, dropping sub-batch): metric/table mismatch: Unable to omit field/column from "measurements": critical column "observed_at"
telegraf-1 | 2025-09-25T14:30:08.010915862Z 2025-09-25T14:30:08Z D! [outputs.postgresql] Wrote batch of 3 metrics in 9.920592ms
telegraf-1 | 2025-09-25T14:30:08.010927570Z 2025-09-25T14:30:08Z D! [outputs.postgresql] Buffer fullness: 0 / 10000 metrics
```

### System info

Telegraf 1.31.6, Ubuntu 24.04, Docker Server 28.4.0, Docker Compose 2.39.4

### Docker

docker-compose.yml

```yaml
services:
postgres:
image: postgres:latest # 17.6-trixie at time of test
environment:
POSTGRES_DB: pgdb
POSTGRES_USER: postgres
POSTGRES_PASSWORD: postgres
ports:
- 5432:5432
volumes:
- ./pg-init.sql:/docker-entrypoint-initdb.d/pg-init.sql
healthcheck:
test: ["CMD-SHELL", "pg_isready -h 127.0.0.1"]
interval: 1m
timeout: 5s
retries: 2
start_period: 3m
start_interval: 5s

telegraf:
image: telegraf:latest # 1.36.1 at time of test
restart: unless-stopped
depends_on:
postgres:
condition: service_healthy
volumes:
- ./telegraf.conf:/etc/telegraf/telegraf.conf
```

pg-init.sql

```sql
create schema core;

create table core.measurements (
observed_at timestamptz NOT NULL
,device_id text NOT NULL
,metric_name text NOT NULL
,metric_value double precision NOT NULL
);

create role ingester login password 'ingester_password';
-- grant usage on schema core to ingester;
-- grant select on core.measurements to ingester;
-- grant insert on core.measurements to ingester;
```

### Steps to reproduce

1. Create the `compose.yml`, `telegraf.conf`, and `pg-init.sql` files provided above.
2. Run `docker compose up -d` to start the containers.
3. Run `docker compose logs -t -f` to view the container logs with timestamps.
4. Note that the postgresql output plugin reports errors (e.g. `E! [outputs.postgresql] write error (permanent, dropping sub-batch): metric/table mismatch: Unable to omit field/column from "measurements": critical column "observed_at"`), but the internal plugin's error counter for the postgresql output plugin isn't incremented (e.g. `internal_write,host=978ec7e2d72e,output=postgresql,version=1.36.1 buffer_limit=10000i,metrics_filtered=10i,startup_errors=0i,metrics_added=3i,metrics_written=3i,metrics_rejected=0i,buffer_size=0i,errors=0i,write_time_ns=78744912i,metrics_dropped=0i 1758810590000000000`).
5. Note that `metrics_written` is being incremented (as shown above), even though none of the `measurements` metrics are being written to the output destination (i.e. the postgres `core.measurements` table).
6. Note that the precise meaning of `metrics_filtered`, `startup_errors`, `metrics_added`, `metrics_written`, `metrics_rejected`, `buffer_size`, `errors`, and `metrics_dropped` is not documented anywhere in the Telegraf Internal plugin [README](https://github.com/influxdata/telegraf/tree/master/plugins/inputs/internal).

### Expected behavior

I expected the `errors` counter and/or `metrics_dropped` and/or `metrics_rejected` counters in the `internal_write,output=postgresql,...` metric to be incremented.

I also expected the `metrics_written` counter not to be incremented (as telegraf was aware that it had failed to write to the output).

That said, I wasn't really sure what to expect, as there are no definitions provided in the [README](https://github.com/influxdata/telegraf/tree/master/plugins/inputs/internal), and previous issues asking for documentation were closed with no public answers provided (e.g. https://github.com/influxdata/telegraf/issues/16809 and https://github.com/influxdata/telegraf/issues/10257)

### Actual behavior

The `errors` counter, `metrics_dropped`, and `metrics_rejected` counters all remained at zero and the `metrics_written` counter was incremented by the number of metrics which were added to the buffer, regardless of whether they were successfully written to the output or not.

### Additional info

Related issues: https://github.com/influxdata/telegraf/issues/16588, https://github.com/influxdata/telegraf/issues/7964, https://github.com/influxdata/telegraf/issues/8607, https://github.com/influxdata/telegraf/issues/16483

Start by reproducing the failure with the provided telegraf.conf, PostgreSQL setup, and outputs.postgresql logs. Trace the postgresql output plugin's error path and internal_write metrics, then verify that the relevant error counter increments when the critical observed_at column error drops a sub-batch.

Written by the indexing model from the issue text.