Basically, you worked with a hotel aggregator that happened to do direct SQL queries for searches. Then you migrated them to this pattern:
"decided to extract the availability search into a separate cache layer based on in-memory data grid (IMDG) platform. This new solution holds in memory a complete set of data required to return a hotel availability information. We also implemented a custom, fast data loading mechanism to populate the memory grid from database as well as a message queue pipeline supporting incremental intraday data updates."
So, putting something like Apache Ignite in place, with intraday updates.
That's an improvement for the client, for sure. But, most hotel aggregators aren't doing live SQL queries against a single database. You happened to find a client that was at the tail end of figuring out that wouldn't scale for them. Any of them with serious volume is doing something similar where they keep the main relational database for data entry and updates. But the live search is done with ElasticSearch, Redis, Geode/Gemfire, Cassandra, plain old read replicas or some other tech that's better suited for the complex availability queries. And some mechanism for intraday updates.