Package buildid provides the build id computation related functions.
Build key: Build keys are autogenerated, monotonically decreasing integers. That is, when sorted by key, new builds are first. Build has no parent.
Build id is a 64 bits integer. - 1 highest order bit is set to 0 to keep value positive. - 43 bits are 43 lower bits of bitwise-inverted time since
beginningOfTheWorld at 1ms resolution. It is good for 2**43 / 365.3 / 24 / 60 / 60 / 1000 = 278 years or 2010 + 278 = year 2288.
- 16 bits are set to a random value. Assuming an instance is internally
consistent with itself, it can ensure to not reuse the same 16 bits in two consecutive requests and/or throttle itself to one request per millisecond. Using random value reduces to 2**-15 the probability of collision on exact same timestamp at 1ms resolution, so a maximum theoretical rate of 65536000 requests/sec but an effective rate in the range of ~64k qps without much transaction conflicts. We should be fine.
- 4 bits are 0. This is to represent the 'version' of the entity
The idea is taken from Swarming TaskRequest entity: https://source.chromium.org/chromium/_/chromium/infra/luci/luci-py/+/a4a91d5e1e14b8b866b68b68bc1055b0b8ffef3b:appengine/swarming/server/task_request.py;l=1380-1404
IdRange converts a creation time range to the build id range. Low/high bounds are inclusive/exclusive respectively for both time and id ranges.