[UNOMI-669] Added more details on sequencing for the migration in the docs (#504)
diff --git a/manual/src/main/asciidoc/migrations/migrate-1.6-to-2.0.adoc b/manual/src/main/asciidoc/migrations/migrate-1.6-to-2.0.adoc
index 9260261..15133a2 100644
--- a/manual/src/main/asciidoc/migrations/migrate-1.6-to-2.0.adoc
+++ b/manual/src/main/asciidoc/migrations/migrate-1.6-to-2.0.adoc
@@ -70,6 +70,14 @@
In most cases, migration steps consist of an Elasticsearch painless script that will handle the data changes.
+Depending of the volume of data, migration can be lengthy. By paying attention to when re-indexation is happening (triggered in the groovy scripts by `MigrationUtils.reIndex()`),
+you can find the most appropriate time for your scritps to be executed and avoid re-indexing the same indices multiple times.
+
+For example if you wanted to update profiles with custom data (currently migrated by `migrate-2.0.0-10-profileReindex.groovy`), you could create a script in position "09" that would only contain painless scripts without a reindexing step.
+The script in position "10" will introduce its own painless script, then trigger the re-indexation. This way you don't have to re-index the same indices twice.
+
+You can find existing painless scripts in https://github.com/apache/unomi/tree/master/tools/shell-commands/src/main/resources/requestBody/2.0.0[tools/shell-commands/src/main/resources/requestBody/2.0.0]
+
At runtime, and when starting the migration, Unomi 2.0 will take its own scripts, any additional scripts located in `data/migration/scripts`, will sort the resulting list alphabetically and execute each migration script sequentially.
==== Perform the migration
@@ -159,6 +167,7 @@
The migration can also be performed using Docker images, the migration itself can be started by passing a specific value to the `KARAF_OPTS` environment variable.
In the context of this migration guide, we will asssume that:
+
- Custom migration scripts are located in `/home/unomi/migration/scripts/`
- Painless scripts, or more generally any migration assets are located in `/home/unomi/migration/assets/`, these scripts will be mounted under `/tmp/assets/` inside the Docker container.
