CDRIVER-4663 Eagerly create minPoolSize connections #1520
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This adds a new public function to the libmongoc API. mongoc_client_pool_warmup "warms up" aka eagerly connects the specified number of clients in a client pool to the MongoDB servers in the pool's topology. This function is thread safe and blocks until the pool contains 'num_to_warmup' clients.
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I am concerned about the generic usefulness of the warmup API. I see this as being primarily motivated by Genny's need to benchmark the server. I expect that is not typical use of the C driver.
Rust has precedent for a client warmup method (mongodb/mongo-rust-driver#932). Though it may not be an apples-to-apples comparison. The Rust driver implements CMAP, which limits the rate of connection creation with maxConnecting. The C driver does not limit the rate of connection creation.
I recommend implementing a pool::warmup in the C++ driver only to limit the new API. This may be a convenience for general users, but I prefer limiting API additions until there is more of a known need. Here is a suggested implementation:
https://github.com/mongodb/mongo-cxx-driver/compare/master...kevinAlbs:mongo-cxx-driver:CDRIVER-4663?expand=1
| bson_t *ping_command = BCON_NEW ("ping", BCON_INT32 (1)); | ||
| size_t num_servers = 0; | ||
| mongoc_server_description_t **descriptions = | ||
| mongoc_client_get_server_descriptions (client, &num_servers); |
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I suggest sending a ping to one server before calling mongoc_client_get_server_descriptions.
mongoc_client_get_server_descriptions does not connect to a server. If server monitoring has not yet returned, I expect it will return the initial set of server descriptions from the URI.
Example: if the URI is mongodb://localhost:27017,localhost:27018, but there are three nodes in the replica set, mongoc_client_get_server_descriptions may only return the two servers in the URI (if monitoring has not yet occurred). Once a hello response is processed from the two known servers, the third server will be added to the topology description.
This is applied in the suggested C++ implementation.
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No longer needed. See CDRIVER-4663. |
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