Pub/Sub: Reduce default publisher batch.maxMilliseconds from 1000 to 100

[kir-titievsky]

A customer reported excessive Publish latency on Pub/Sub: consistently over 1 second. On closer inspection, it turned out that the user intended to publish one messages at a time, each from its own invocation of a Cloud Function. Since by default the batching settings were set to wait for 1000 ms [1], the user had observed a shockingly bad latency.

I propose changing the default to 100 ms as it offers reasonable buffering in high throughput cases (most publish requests take fewer than 100ms to complete) and prevent excessively high latency with default settings for these one-off cases.

[1]

nodejs-pubsub/src/publisher.js

Line 60 in 53f1505

maxMilliseconds: 1000,