The ETag HTTP response header is a unique identifier assigned to a specific version of a resource on a server. When a resource, like a web page or an API endpoint, changes, its ETag also changes. This mechanism allows client-side caching and efficient revalidation.
When a client requests a resource, it may include the ETag it has in an If-None-Match request header. If the server's current version of the resource has a matching ETag, it means the content hasn't changed, and the server can send back a 304 Not Modified response without the actual resource data.
This saves bandwidth and speeds up the loading process, as the client can use its cached version. When the ETags don't match, it indicates the resource has changed, prompting the server to send the new version of the resource with its updated ETag.
All ETag values are cached to make ETag queries efficient. If you somehow made this cache invalid, you can reset Aidbox ETag cache by DELETE /$etags-cache or DELETE /Patient/$etags-cache.
The Aidbox ETags mechanism is based on txid column of the resource table in the database! If you update resources in the database, don't forget to update the txid column and reset cache. UPDATE resource SET txid = nextval('transaction_id_seq')
ETag Cache performance
To build a cache for a specific resourceType ETag Aidbox runs a query to get the max value of the txid column. To make this operation efficient, it's recommended to build an index on the txid column for tables where ETag will be used.
replace with table name, for example CREATE INDEX IF NOT EXISTS patient_txid_btree ON patient using btree(txid); CREATE INDEX IF NOT EXISTS patient_history_txid_btree ON patient_history using btree(txid);