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ircd:Ⓜ️:fed: Improve cache characteristic for fallback on expired records.

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This commit is contained in:
Jason Volk 2020-04-27 22:12:26 -07:00
parent 7f4da633f3
commit 4c8e306a94
1 changed files with 22 additions and 5 deletions
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27
matrix/fed.cc
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@ -1731,7 +1731,6 @@ try
const bool expired
{
ircd::now<system_point>() > expires
|| empty(cached)
};
// Crucial value that will provide us with a return string for this
@ -1740,10 +1739,9 @@ try
// when a network query needs to be made, otherwise we can return the
// cached value. If the network query fails, this value is still defaulted
// as the origin string to return and we'll also cache that too.
assert(expired || !empty(cached));
const string_view delegated
{
expired?
empty(cached) || expired?
fetch_well_known(buf, origin):
// Move the returned string to the front of the buffer; this overwrites
@ -1755,9 +1753,9 @@ try
};
// Branch on valid cache hit to return result.
if(!expired)
if(!empty(cached) && !expired)
{
thread_local char tmbuf[48];
char tmbuf[48];
log::debug
{
well_known_log, "%s found in cache delegated to %s event_idx:%u expires %s",
@ -1770,6 +1768,25 @@ try
return delegated;
}
// Branch on query failure to fallback on existing expired record
if(expired && !empty(cached) && delegated == origin)
{
char tmbuf[48];
log::debug
{
well_known_log, "%s fallback to cached delegation to %s event_idx:%u expired %s",
origin,
cached,
event_idx,
timef(tmbuf, expires, localtime),
};
return string_view
{
data(buf), move(buf, cached)
};
}
// Any time the well-known result is the same as the origin (that
// includes legitimate errors where fetch_well_known() returns the
// origin to default) we consider that an error and use the error