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web: Use better exponential backoff algorithm. 

This matches the algorithm that we designed for the Python API, except
that we use a ratio of 2 rather than sqrt(2) in the message_fetch code
path, because it's a heavier request.

We increase the number of failures before showing a user-facing error
to roughly preserve the same time period before a user-facing error is
shown.
This commit is contained in:
Tim Abbott 2024-02-02 14:12:40 -08:00
parent e3960c22be
commit b5b496c752
2 changed files with 11 additions and 7 deletions
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9
web/src/message_fetch.js
View File

@ -377,11 +377,10 @@ export function load_messages(opts, attempt = 1) {
// the server is giving us 500s/502s. // the server is giving us 500s/502s.
// //
// So we do the maximum of the retry-after header and an exponential // So we do the maximum of the retry-after header and an exponential
// backoff with full jitter: up to 2s, 4s, 8s, 16s, 32s // backoff with ratio 2 and half jitter. Starts at 1-2s and ends at
let backoff_delay_secs = Math.random() * 2 ** attempt * 2; // 16-32s after 5 failures.
if (attempt >= 5) { const backoff_scale = Math.min(2 ** attempt, 32);
backoff_delay_secs = 30; const backoff_delay_secs = ((1 + Math.random()) / 2) * backoff_scale;
}
let rate_limit_delay_secs = 0; let rate_limit_delay_secs = 0;
if (xhr.status === 429 && xhr.responseJSON?.code === "RATE_LIMIT_HIT") { if (xhr.status === 429 && xhr.responseJSON?.code === "RATE_LIMIT_HIT") {
// Add a bit of jitter to the required delay suggested by the // Add a bit of jitter to the required delay suggested by the

9
web/src/server_events.js
View File

@ -231,7 +231,7 @@ function get_events({dont_block = false} = {}) {
get_events_failures += 1; get_events_failures += 1;
} }
if (get_events_failures >= 5) { if (get_events_failures >= 8) {
show_ui_connection_error(); show_ui_connection_error();
} else { } else {
hide_ui_connection_error(); hide_ui_connection_error();
@ -243,7 +243,12 @@ function get_events({dont_block = false} = {}) {
// We need to respect the server's rate-limiting headers, but beyond // We need to respect the server's rate-limiting headers, but beyond
// that, we also want to avoid contributing to a thundering herd if // that, we also want to avoid contributing to a thundering herd if
// the server is giving us 500s/502s. // the server is giving us 500s/502s.
const backoff_delay_secs = Math.min(90, Math.exp(get_events_failures / 2)); //
// So we do the maximum of the retry-after header and an exponential
// backoff with ratio sqrt(2) and half jitter. Starts at 1-2s and ends at
// 45-90s after enough failures.
const backoff_scale = Math.min(2 ** ((get_events_failures + 1) / 2), 90);
const backoff_delay_secs = ((1 + Math.random()) / 2) * backoff_scale;
let rate_limit_delay_secs = 0; let rate_limit_delay_secs = 0;
if (xhr.status === 429 && xhr.responseJSON?.code === "RATE_LIMIT_HIT") { if (xhr.status === 429 && xhr.responseJSON?.code === "RATE_LIMIT_HIT") {
// Add a bit of jitter to the required delay suggested // Add a bit of jitter to the required delay suggested