[tor-bugs] #22421 [Core Tor/Tor]: Update fallback config comment for exponential backoff

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#22421: Update fallback config comment for exponential backoff
-------------------------------+------------------------------------
 Reporter:  teor               |          Owner:
     Type:  defect             |         Status:  needs_review
 Priority:  Medium             |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor       |        Version:  Tor: 0.2.9.1-alpha
 Severity:  Normal             |     Resolution:
 Keywords:  fallback, comment  |  Actual Points:  0.1
Parent ID:                     |         Points:  0.1
 Reviewer:                     |        Sponsor:
-------------------------------+------------------------------------
Changes (by teor):

 * status:  new => needs_review


Old description:

> We modified the fallback behaviour when we merged the exponential backoff
> code in 0.2.9.1-alpha, and again in #17750:
> {{{
> /* With the ClientBootstrapConsensus*Download* below:
>    * Clients with only authorities will try:
>    *  - 3 authorities over 10 seconds, then wait 60 minutes.
>    * Clients with authorities and fallbacks will try:
>    *  - 2 authorities and 4 fallbacks over 21 seconds, then wait 60
> minutes.
>    * Clients will also retry when an application request arrives.
>    * After a number of failed reqests, clients retry every 3 days + 1
> hour.
>    *
>    * Clients used to try 2 authorities over 10 seconds, then wait for
>    * 60 minutes or an application request.
>    *
>    * When clients have authorities and fallbacks available, they use
> these
>    * schedules: (we stagger the times to avoid thundering herds) */
>   V(ClientBootstrapConsensusAuthorityDownloadSchedule, CSV_INTERVAL,
>     "6, 11, 3600, 10800, 25200, 54000, 111600, 262800" /* 3 days + 1 hour
> */),
>   V(ClientBootstrapConsensusFallbackDownloadSchedule, CSV_INTERVAL,
>     "0, 1, 4, 11, 3600, 10800, 25200, 54000, 111600, 262800"),
>   /* When clients only have authorities available, they use this
> schedule: */
>   V(ClientBootstrapConsensusAuthorityOnlyDownloadSchedule, CSV_INTERVAL,
>     "0, 3, 7, 3600, 10800, 25200, 54000, 111600, 262800"),
> }}}
>
> The behaviour is now:
> {{{
> /* With the ClientBootstrapConsensus*Download* below:
>    * Clients with only authorities will try:
>    *  - at least 3 authorities over 10 seconds, then exponentially
> backoff, with the next attempt 3-21 seconds later,
>    * Clients with authorities and fallbacks will try:
>    *  - at least 2 authorities and 4 fallbacks over 21 seconds, then
> exponentially backoff, with the next attempts 4-33 seconds later,
>    * Clients will also retry when an application request arrives.
>    * After a number of failed reqests, clients retry every 3 days + 1
> hour.
>    *
>    * Clients used to try 2 authorities over 10 seconds, then wait for
>    * 60 minutes or an application request.
> }}}

New description:

 We modified the fallback behaviour when we merged the exponential backoff
 code in 0.2.9.1-alpha, and again in #17750:
 {{{
 /* With the ClientBootstrapConsensus*Download* below:
    * Clients with only authorities will try:
    *  - 3 authorities over 10 seconds, then wait 60 minutes.
    * Clients with authorities and fallbacks will try:
    *  - 2 authorities and 4 fallbacks over 21 seconds, then wait 60
 minutes.
    * Clients will also retry when an application request arrives.
    * After a number of failed reqests, clients retry every 3 days + 1
 hour.
    *
    * Clients used to try 2 authorities over 10 seconds, then wait for
    * 60 minutes or an application request.
    *
    * When clients have authorities and fallbacks available, they use these
    * schedules: (we stagger the times to avoid thundering herds) */
   V(ClientBootstrapConsensusAuthorityDownloadSchedule, CSV_INTERVAL,
     "6, 11, 3600, 10800, 25200, 54000, 111600, 262800" /* 3 days + 1 hour
 */),
   V(ClientBootstrapConsensusFallbackDownloadSchedule, CSV_INTERVAL,
     "0, 1, 4, 11, 3600, 10800, 25200, 54000, 111600, 262800"),
   /* When clients only have authorities available, they use this schedule:
 */
   V(ClientBootstrapConsensusAuthorityOnlyDownloadSchedule, CSV_INTERVAL,
     "0, 3, 7, 3600, 10800, 25200, 54000, 111600, 262800"),
 }}}

 The behaviour is now:
 {{{
 /* With the ClientBootstrapConsensus*Download* below:
    * Clients with only authorities will try:
    *  - at least 3 authorities over 10 seconds, then exponentially
 backoff, with the next attempt 3-21 seconds later,
    * Clients with authorities and fallbacks will try:
    *  - at least 2 authorities and 4 fallbacks over 21 seconds, then
 exponentially backoff, with the next attempts 4-33 seconds later,
    * Clients will also retry when an application request arrives.
    * After a number of failed requests, clients retry every 3 days + 1
 hour.
    *
    * Clients used to try 2 authorities over 10 seconds, then wait for
    * 60 minutes or an application request.
 }}}

--

Comment:

 Edit: let's fix a typo in that comment as well.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22421#comment:1>
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