*NOTE: This Poppy Jira is cloned by Orchid CSP 5 Jira MODSOURCE-671* MODSOURCE-601 introduced a notion of 'version' in marc_indexers table to allow inserts of new rows without deletion (deletion is done as a separate process). Setting the initial version (zero) to all existing rows takes excess time during which DI (and other processes interacting with SRS) should be suspended. Allow DI and search of marc_indexers to function correctly when version is still null (column added, but values are not there yet), treat it as a zero.  * Search when no other version than null  * Insert of new values with version '1', when others are null * Something else? *ORCHID Critical service patch details* # *Describe issue impact on business:* Required to be able to backport the improvements described in MODSOURCE-601/MODSOURCE-654 to Orchid. This change allows DI marc-to-marc matching and records search to work correctly until migration scripts which are required by MODSOURCE-601MODSOURCE-654 are completed, in order to avoid downtime during the those scripts execution. # *What institutions are affected? (field “Affected Institutions” in Jira to be populated) -* All # *What is the workaround if exists?* No user workaround # *What areas will be impacted by fix (i.e. what areas need to be retested)* Data import Smoke and Critical path tests # *Brief explanation of technical implementation and the level of effort (in workdays) and technical risk (low/medium/high).* ** Work is complete and the level of effort was medium.  ** Approach *** add alternative/fallback query that performs a search without indexers version usage to DAO method that provides marc-to-marc matching and to the method aimed for retrieving marc identifiers by search query. This alternative query should be executed when the search results of the current queries are empty and newly introduced parameter srs.record.matching.fallback-query.enable = true. *** fix PgException handling in AbstractUpdateModifyEventHandler to prevent import job from being stuck if PgException is not related to matchedId-generation uniqueness constraint violation. *** add tests ** Risk to backport: Minimal; [~accountid:712020:8112ce6a-772f-4888-afd3-b243105d06aa] will also review with [~accountid:70121:329e0f11-cc86-459e-a311-80d4eb134a7f] # *Brief explanation of testing required and level of effort (in workdays). Provide test plan agreed with by QA Manager and PO.* Automated test cases already exist and level of effort is 1 hour # *What is the roll back plan in case the fix does not work?* Revert to previous version