The Endeca Server processes two types of queries — non-updating (or read-only) queries, and updating queries.
- The purpose of non-updating queries is, typically, to obtain query results from the index, based on search or navigation selections made by the end users in the front-end application. Non-updating queries represent read-only requests to the index and do not attempt to change them.
- The purpose of updating queries is to change the index or other settings in the data domain or the Dgraph process. Updating queries represent "write" requests to the index.
The following diagram shows how both updating and non-updating queries are processed by the Endeca Server in view of outer transactions. It illustrates that, to be processed within an outer transaction, updating queries must specify its ID. Non-updating queries, depending on whether they specify the outer transaction ID, are processed against different versions of the index:
The following statements describe the actions in this diagram in detail,
starting from the left side of the diagram:
- Stage 1: Before an outer transaction is started. If no outer transaction is in progress, then all queries (updating and non-updating) are processed against the most recent published version of the index. If no outer transaction is in progress, the queries do not need to specify any outer transaction ID.
- Stage 2: The outer
transaction has been started. Queries that specify a correct outer
transaction ID (also known as queries sent inside the transaction):
- All such queries (updating and non-updating) are guaranteed to run against the most recent internal version of the index available to the transaction. This version is not published and not available to queries outside of the outer transaction until the transaction commits. This version is published after the transaction commits.
Queries that do not specify an outer transaction ID (also known as queries sent outside of the transaction):- Non-updating queries run against the most recent published (pre-transaction) version of the index.
- Updating queries wait until the outer transaction is committed (or rolled back), and are computed based on the published version of the index available at that time.
If the outer transaction has been started and requests sent to the Endeca Server specify an incorrect ID, the requests fail.
- Stage 3: After the outer transaction has been committed. All queries (updating and non-updating) are processed against the most recent published version of the index.
