collector.stat_statements.query_length does not truncate properly

[jsadowyj]

What did you do?
Enabled the following collector options:

 - collector.stat_statements.include_query
 - collector.stat_statements.query_length=4000

What did you expect to see?
The query label is truncated to 4000 characters (including comments).

What did you see instead? Under which circumstances?

pg_stat_statements_block_read_seconds_total{datname="<redacted>",queryid="-5016773285470984866",user="metabase_ro"} 0
pg_stat_statements_block_write_seconds_total{datname="<redacted>",queryid="-5016773285470984866",user="metabase_ro"} 0
pg_stat_statements_calls_total{datname="<redacted>",queryid="-5016773285470984866",user="metabase_ro"} 5
pg_stat_statements_query_id{query="-- Metabase:: userID: 1 queryType: MBQL queryHash: 54162c2fced7fe3932b12602637694179314c62f535f392cbd3cea208aec60d2\nSELECT \"public\".\"notifications\".\"id\" AS \"id\", (\"public\".\"notifications\".\"metadata\"#>> array[$1]::text[])::text AS \"metadata → body\", (\"public\".\"notifications\".\"metadata\"#>> array[$2]::text[])::text AS \"metadata → data\", (\"public\".\"notifications\".\"metadata\"#>> array[$3, $4]::text[])::text AS \"metadata → data → amount\", (\"public\".\"notifications\".\"metadata\"#>> array[$5, $6]::text[])::text AS \"metadata → data → platform_type\", (\"public\".\"notifications\".\"metadata\"#>> array[$7, $8]::text[])::text AS \"metadata → data → receiver\", (\"public\".\"notifications\".\"metadata\"#>> array[$9, $10, $11]::text[])::text AS \"metadata → data → receiver → avatar\", (\"public\".\"notifications\".\"metadata\"#>> array[$12, $13, $14]::text[])::text AS \"metadata → data → receiver → first_name\", (\"public\".\"notifications\".\"metadata\"#>> array[$15, $16, $17]::text[])::text AS \"metadata → data → receiver → id\", (\"public\".\"notifications\".\"metadata\"#>> array[$18, $19, $20]::text[])::text AS \"metadata → data → receiver → last_name\", (\"public\".\"notifications\".\"metadata\"#>> array[$21, $22, $23]::text[])::text AS \"metadata → data → receiver → username\", (\"public\".\"notifications\".\"metadata\"#>> array[$24, $25, $26]::text[])::text AS \"metadata → data → sender → first_name\", (\"public\".\"notifications\".\"metadata\"#>> array[$27, $28, $29]::text[])::text AS \"metadata → data → sender → id\", (\"public\".\"notifications\".\"metadata\"#>> array[$30, $31, $32]::text[])::text AS \"metadata → data → sender → last_name\", (\"public\".\"notifications\".\"metadata\"#>> array[$33, $34, $35]::text[])::text AS \"metadata → data → sender → username\", (\"public\".\"notifications\".\"metadata\"#>> array[$36, $37, $38]::text[])::text AS \"metadata → data → transaction → amount\", (\"public\".\"notifications\".\"metadata\"#>> array[$39, $40, $41]::text[])::text AS \"metadata → data → transaction → amountUsd\", (\"public\".\"notifications\".\"metadata\"#>> array[$42, $43, $44]::text[])::text AS \"metadata → data → transaction → blockExplorerLink\", (\"public\".\"notifications\".\"metadata\"#>> array[$45, $46, $47]::text[])::text AS \"metadata → data → transaction → from\", (\"public\".\"notifications\".\"metadata\"#>> array[$48, $49, $50]::text[])::text AS \"metadata → data → transaction → gasFee\", (\"public\".\"notifications\".\"metadata\"#>> array[$51, $52, $53, $54]::text[])::text AS \"metadata → data → transaction → original → error\", (\"public\".\"notifications\".\"metadata\"#>> array[$55, $56, $57]::text[])::text AS \"metadata → data → transaction → to\", (\"public\".\"notifications\".\"metadata\"#>> array[$58, $59, $60]::text[])::text AS \"metadata → data → transaction → transactionHash\", (\"public\".\"notifications\".\"metadata\"#>> array[$61, $62]::text[])::text AS \"metadata → data → transaction_hash\", (\"public\".\"notifications\".\"metadata\"#>> array[$63, $64]::text[])::text AS \"metadata → data → ulid\", (\"public\".\"notifications\".\"metadata\"#>> array[$65]::text[])::text AS \"metadata → event\", (\"public\".\"notifications\".\"metadata\"#>> array[$66]::text[])::text AS \"metadata → notification_type\", (\"public\".\"notifications\".\"metadata\"#>> array[$67, $68]::text[])::text AS \"metadata → payload → amount\", (\"public\".\"notifications\".\"metadata\"#>> array[$69, $70]::text[])::text AS \"metadata → payload → chainId\", (\"public\".\"notifications\".\"metadata\"#>> array[$71, $72]::text[])::bigint AS \"metadata → payload → creationHeight\", (\"public\".\"notifications\".\"metadata\"#>> array[$73, $74]::text[])::text AS \"metadata → payload → description\", (\"public\".\"notifications\".\"metadata\"#>> array[$75, $76]::text[])::text AS \"metadata → payload → from\", (\"public\".\"notifications\".\"metadata\"#>> array[$77, $78]::text[])::text AS \"metadata → payload → memo\", (\"public\".\"notifications\".\"metadata\"#>> array[$79, $80]::text[])::text AS \"metadata → payload → symbol\", (\"public\".\"notifications\".\"metadata\"#>> array[$81, $82]::text[])::text AS \"metadata → payload → to\", (\"public\".\"notifications\".\"metadata\"#>> ar",queryid="-5016773285470984866"} 1
pg_stat_statements_rows_total{datname="<redacted>",queryid="-5016773285470984866",user="metabase_ro"} 10000
pg_stat_statements_seconds_total{datname="<redacted>",queryid="-5016773285470984866",user="metabase_ro"} 42.436016087

The label length always exceeds 4000 bytes for the above query:

$ pbpaste | wc -c
    4451

Environment

• System information:

# uname -srm
Linux 6.8.0-35-generic x86_64

• postgres_exporter version:

# postgres_exporter --version
postgres_exporter, version 0.18.1 (branch: HEAD, revision: 320b684f3dcd3f09b6e694e43f9b389b1a8199e5)
  build user:       root@83cf77f7d3ab
  build date:       20250929-17:16:35
  go version:       go1.24.7
  platform:         linux/amd64
  tags:             unknown

• postgres_exporter flags:

usr/local/bin/postgres_exporter \
    --collector.stat_statements \
    --collector.stat_statements.include_query \
    --collector.stat_statements.query_length=4000 \
    --collector.replication \
    --collector.replication_slot \
    --collector.stat_wal_receiver \
    --web.listen-address=0.0.0.0:9187 \
    --config.file=/etc/postgres_exporter/postgres_exporter.yml \
    --web.telemetry-path=/metrics

• PostgreSQL version:

postgres=# select version();
                                                         version
--------------------------------------------------------------------------------------------------------------------------
 PostgreSQL 15.10 - Percona Distribution on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 13.2.0-23ubuntu4) 13.2.0, 64-bit
(1 row)

• Logs:

None to speak of.