What are expensive queries in The Graph indexer node?

An expensive query refers to a query that is more complex or resource-intensive. While an indexer would be able to provide a more detailed explanation, I can offer some insights. There are a few reasons why a query might be considered expensive:

1. Subgraph optimization: If a subgraph is not properly optimized or contains a large number of entities, it can result in a higher cost to query. Subgraphs that are well-optimized can provide faster and more efficient queries, reducing the associated costs.

2. Complex queries: Another factor that can contribute to an expensive query is the complexity of the query itself. For example, searching for information on all NFTs can involve a significant amount of data retrieval, resulting in higher costs.

It's important to note that the cost of a query is typically measured in terms of Graph Tokens (GRT), the native token of The Graph protocol. The more resources required to execute a query, the more GRT it will cost.

In summary, an expensive query is one that is more complicated or resource-intensive, either due to subgraph optimization issues or the complexity of the query itself. Optimized subgraphs and well-designed queries can help reduce the costs associated with querying The Graph protocol.