Two changes on the push path, both measured against a real Stalwart 0.16.20
with the container capped at 256 MiB and tabs added in steps of 200 until the
kernel killed it:
tabs held per tab of which native
before 1,665 133 KiB 81 KiB
pin upstream calls to STALWART_URL 3,400 58 KiB 8 KiB
+ raw push relay 4,979 37 KiB 10 KiB
Stalwart advertises absolute https URLs in every session, and the proxy
followed them -- so even with STALWART_URL naming a private plain-HTTP hop on
the same Docker network, every held push stream went out through TLS. That leg
is about 80 KiB of OpenSSL state per tab: native memory Node cannot see, which
is why neither the heap ceiling nor the stream buffer size ever moved the
number. absoluteUpstream() now keeps the path and query from the advertised
URL and the scheme, host and port from the configured one. A setup that must
reach Stalwart at an origin other than the one it was given sets
STALWART_FOLLOW_ADVERTISED_URLS=1.
With the transport out of the way, the fetch()-based relay was the next cost:
an undici Response, a web ReadableStream, a reader and Hono's stream bridge
held alive per tab, about 44 KiB of heap for a session that otherwise costs
4 KiB. relayPushRaw() pipes the upstream socket into the Node response and
tells the adapter the response is already sent. RAW_PUSH_RELAY=0 restores the
fetch path for comparison.
JMAP throughput is unchanged (2,383/s against 2,484/s at 50 users, inside
run-to-run noise); the relay does not touch that path. Verified that a push
stream through the raw relay delivers a StateChange while mail is written.
The install page's advice to set --max-old-space-size was measured in the same
runs and made no difference at all -- 3,400 tabs with it and without -- and
is withdrawn in the docs alongside this change.
jcoffey-dev
01f721d8d1