Tom Fitzhenry created HTTPCORE-424:
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Summary: A means to keep connections alive, even if fewer
connections would suffice
Key: HTTPCORE-424
URL: https://issues.apache.org/jira/browse/HTTPCORE-424
Project: HttpComponents HttpCore
Issue Type: New Feature
Components: HttpCore NIO
Reporter: Tom Fitzhenry
Priority: Minor
h3. Usecase
I make 500req/s to the same server, whose response times average 5ms. This only
needs 3 connections. This 500req/s occasionally bursts to 1000req/s, but as I
only have 3 connections in my connection pool, I then have to establish a bunch
of connections (let's say 17), at which point the latency suffers the cost of a
TCP/SSL handshake.
The rate then drops to the baseline 500req/s, but next time the 1000req/s burst
occurs, I'll be ready right?! I have 20 connections in my pool, waiting for me
to need them.
No, I won't be ready. By the time the burst occurs, these extra connections
have timed out, because they've not been used, and these connections are
subject to TCP and HTTP time outs (both beyond my control).
It would be nice to have a way to keep these connections active, so they don't
idle out, ready for when I next see a burst of 1000req/s.
h3. A possible implementation:
A simple implementation would be to lease connections on a FIFO basis, rather
than a LIFO basis (Apache HttpAsyncClient's current behaviour). With a FIFO
policy, all connections would be kept active, so they would never idle out.
Apache HttpAsyncClient uses a LinkedList, in LIFO mode: lines 83 and 129 of
https://github.com/apache/httpcore/blob/4.4.x/httpcore-nio/src/main/java/org/apache/http/nio/pool/RouteSpecificPool.java#L83
h3. Other HTTP clients:
RxJava uses a Queue (FIFO):
https://github.com/ReactiveX/RxJava/blob/2a8d6c75205b13cd9bef2b7f7d47723e1c86454e/src/main/java/rx/internal/util/ObjectPool.java#L28
Vert.x uses a Queue (FIFO):
https://github.com/eclipse/vert.x/blob/dbdcb3c785e9d8ff70dcce6a2e148cd3da6d15f6/src/main/java/io/vertx/core/http/impl/Http1xPool.java#L48
async-http-client allows user to specify LIFO or FIFO:
https://github.com/AsyncHttpClient/async-http-client/issues/1184
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