> 1. The upgrade process[1] suggests an N+/-1 compat story, e.g. 8.11.2 should > be able to co-mingle with 7.>3 but I haven't turned up any firm statements > about that.
Yes, rolling upgrade from 7.x (recommend first going to latest 7.x) to 8.x is possible as outlined here https://solr.apache.org/guide/solr/latest/upgrade-notes/major-changes-in-solr-8.html#rolling-upgrades-with-solr-8. You should carefully audit all the upgrade notes before starting. However, this assumes your collection was initially made on 7.x. If your index was made on earlier version, e.g. 6.x and then upgraded to 7.x, then you cannot upgrade to 8.x and should re-index from scratch. This is also documented. By simulating the full upgrade procedure on your test / QA cluster first you can weed out any issues before heading to your prod cluster. The recommendation is however to install a brand new 9.0 cluster (since 8.x will be EOL within a year) and re-index. > 2. Is there forward/backward compatibility between segment/index files > between version? e.g. we have automatic core recovery from backups in the > event that a node fails. If I'm running a v8 node that fails after a backup > has been taken and the core gets restored to a v7 does that sound > problematic? (I'm guessing maybe/yes per [3]) If the restore is an index created with 7.x, no issues, see above. > 3. the docs refer to IndexUpgraderTool[2] but nothing indicates when/if I > should be running this manually as far as I can tell. How does this come into > play? Don't use that tool. Solr 8 is capable of reading v7 indices, so no need. And if your index was first created in 6.x, and you go ahead using the upgrader tool to get it to 7.x and then 8.x, then Solr8 would refuse to start since it will find traces of v6.x in the binary index files. > And of course if there are any docs it sounds like I may have missed (or > useful threads / issues / whatever) comes to mind that I should read feel > free to point me at them. Most of what you'll need is here https://solr.apache.org/guide/8_11/solr-upgrade-notes.html and for 9.0 here https://solr.apache.org/guide/solr/latest/upgrade-notes/solr-upgrade-notes.html The reindexing page is also useful https://solr.apache.org/guide/solr/latest/indexing-guide/reindexing.html In particular the "Upgrades" section https://solr.apache.org/guide/solr/latest/indexing-guide/reindexing.html#upgrades Jan
