Recently the team were asked about potential upgrade paths from Solr 4 to different versions of Search Services. This page aims to look specifically at upgrading and reindexing across various versions of our search products. Some noteworthy upgrade paths are shown in this diagram:
Some potential upgrade paths showing versions of ACS and where reindexes are required.
All Search Services versions are based on Solr 6 (at time of writing), and so an existing Solr 4 index cannot be reused. If an ACS upgrade is required then this must be done before the reindexing can start (because populating e.g. Search Services 2.0.x is not supported with ACS 5.x).
It is possible to upgrade from Search Services 1.3.x to Search Services 126.96.36.199 without a reindex - they are both based on Solr 6 and the index structure has not changed significantly. However there are some performance improvements in 188.8.131.52 which will not be seen without a reindex (or they will only effect new documents).
Many versions of Search Services and Insight Engine are not shown in the diagram. However the other versions are broadly similar to those shown:
Search Services 1.0.x-1.2.x and Insight Engine 1.0.x-1.1.x act similarly to Search Services 1.3.x;
Search Services and Insight Engine 1.4.0-184.108.40.206 act similarly to Search Services 220.127.116.11, but do not contain important performance fixes.
A large compatibility matrix is given at the end of the post.
In a large system (e.g. tens of millions of documents) then the reindexing process can take many days. This will usually not be acceptable downtime for search and so it's important to reindex in parallel using a separate system from the production system. More information about this and other related topics can be found in the Tech Talk Live presentation “(Re)Indexing Large Repositories in Alfresco”:
If you're interested in upgrading to Search Services or Insight Engine 2.0 specifically, then the Tech Talk Live "Discovering the '2' in Search Services 2.0" contains further information about why reindexing is necessary when upgrading to 2.0.
The official docs site contains information about which versions of ACS are compatible with each version of search, but this information is spread across several pages. Here we show the same information in a more concise table: