Adding the section on dangling sessions to the bigquery page

	modified:   docs/sdk/resources/persisting-data/bigquery.md

docs/sdk/resources/persisting-data/bigquery.md

@@ -75,3 +75,44 @@ deploy:
 ## Examples
 
 An end-to-end example geared towards local runs can be found in [this repo](https://github.com/subsquid-labs/squid-bigquery-example). Look at [this branch](https://github.com/subsquid-labs/squid-bigquery-example/tree/cloud-secrets) for an example of a squid made for deployment to SQD Cloud.
+
+## Troubleshooting
+
+### Transaction is aborted due to concurrent update
+
+This means that your project has an open [session](https://cloud.google.com/bigquery/docs/sessions-intro) that is updating some of the tables used by the squid.
+
+Most commonly, the session is left by a squid itself after an unclean termination. You have two options:
+
+1. If you are not sure if your squid is the only app that uses sessions to access your BigQuery project, find the faulty session manually and terminate it. See [Get a list of your active sessions](https://cloud.google.com/bigquery/docs/sessions-get-ids#list_active) and [Terminate a session by ID](https://cloud.google.com/bigquery/docs/sessions-terminating#terminate_a_session_by_id).
+
+2. **DANGEROUS** If you are absolutely certain that the squid is the only app that uses sessions to access your BigQuery project, you can terminate all the dangling sessions by running
+
+   ```sql
+   FOR session in (
+     SELECT
+       session_id,
+       MAX(creation_time) AS last_modified_time,
+     FROM `region-us`.INFORMATION_SCHEMA.SESSIONS_BY_PROJECT
+     WHERE
+       session_id IS NOT NULL
+       AND is_active
+     GROUP BY session_id
+     ORDER BY last_modified_time DESC
+   )
+   DO
+     CALL BQ.ABORT_SESSION(session.session_id);
+   END FOR;
+   ```
+   Replace `region-us` with your dataset's region in the code above.
+
+   You can also enable `abortAllProjectSessionsOnStartup` and supply `datasetRegion` in your database config to perform this operation at startup:
+   ```ts
+   const db = new Database({
+     // ...
+     abortAllProjectSessionsOnStartup: true,
+     datasetRegion: 'region-us'.
+   })
+   ```
+
+   This method **will** cause data loss if, at the moment when the squid starts, some other app happens to be writing data anywhere in the project using the sessions mechanism.