Update WAL_*_TXN metrics names

documentation/operations/monitoring-alerting.md

@@ -3,7 +3,11 @@ title: Monitoring and alerting
 description: Shows you how to set up to monitor your database for potential issues, and how to raise alerts
 ---
 
-There are many variables to consider when monitoring an active production database. This document is designed to be a helpful starting point. We plan to expand this guide to be more helpful. If you have any recommendations, feel free to [create an issue](https://github.com/questdb/documentation/issues) or a PR on GitHub. 
+There are many variables to consider when monitoring an active production
+database. This document is designed to be a helpful starting point. We plan to
+expand this guide to be more helpful. If you have any recommendations, feel free
+to [create an issue](https://github.com/questdb/documentation/issues) or a PR on
+GitHub.
 
 ## Basic health check
 
@@ -55,8 +59,8 @@ take longer if the data is out of order, or touches different time partitions.
 You can monitor the overall performance of this process of applying the WAL
 data to tables. QuestDB exposes two Prometheus counters for this:
 
-1. `questdb_wal_apply_seq_txn_total`: sum of all committed transaction sequence numbers
-2. `questdb_wal_apply_writer_txn_total`: sum of all transaction sequence numbers applied to tables
+1. `questdb_wal_apply_seq_txn`: sum of all committed transaction sequence numbers
+2. `questdb_wal_apply_writer_txn`: sum of all transaction sequence numbers applied to tables
 
 Both of these numbers are continuously growing as the data is ingested. When
 they are equal, all WAL data has been applied to the tables. While data is being

documentation/third-party-tools/prometheus.md

@@ -241,11 +241,14 @@ The following metrics are available:
 | `questdb_wal_apply_rows_per_second`               | gauge   | Rate of rows applied per second during WAL apply.                                                                                                                                                           |
 | `questdb_wal_apply_written_rows_total`            | counter | Total number of rows written during WAL apply.                                                                                                                                                              |
 | `questdb_wal_written_rows_total`                  | counter | Total number of rows written to WAL.                                                                                                                                                                        |
+| `questdb_wal_seq_txn`                             | gauge   | Sum of all committed transaction sequence numbers. Used in conjunction with `questdb_wal_writer_txn`.                                                                                                       |
+| `questdb_wal_writer_txn`                          | gauge   | Sum of all transaction sequence numbers applied to tables. With no pending transactions in the WAL, equal to `questdb_wal_seq_txn`. When its lag behind `questdb_wal_seq_txn` is steadily growing, indicates QuestDB is unable to keep up with writes. |
 | `questdb_workers_job_start_micros_max`            | gauge   | Maximum time taken to start a worker job in microseconds.                                                                                                                                                   |
 | `questdb_workers_job_start_micros_min`            | gauge   | Minimum time taken to start a worker job in microseconds.                                                                                                                                                   |
 
-All of the above metrics are volatile, i.e. they're collected since the current
-database start.
+Most of the above metrics are volatile, i.e. they're collected since the current
+database start. The exception are `questdb_wal_seq_txn` and
+`questdb_wal_writer_txn`, because transaction sequence numbers are persistent.
 
 ## Configuring Prometheus Alertmanager