Merge cockroachdb#35765

35765: storage: temporarily disable follower reads by default r=ajwerner a=ajwerner

It seems that enabling follower reads combined with recent changes to make
follower reads more likely in the face of lease transfers has led to some
test flakes. This PR disables follower reads by default for the time being

Release note: None

Co-authored-by: Andrew Werner <[email protected]>

docs/generated/settings/settings.html

@@ -33,7 +33,7 @@
 <tr><td><code>kv.bulk_io_write.max_rate</code></td><td>byte size</td><td><code>8.0 EiB</code></td><td>the rate limit (bytes/sec) to use for writes to disk on behalf of bulk io ops</td></tr>
 <tr><td><code>kv.bulk_sst.sync_size</code></td><td>byte size</td><td><code>2.0 MiB</code></td><td>threshold after which non-Rocks SST writes must fsync (0 disables)</td></tr>
 <tr><td><code>kv.closed_timestamp.close_fraction</code></td><td>float</td><td><code>0.2</code></td><td>fraction of closed timestamp target duration specifying how frequently the closed timestamp is advanced</td></tr>
-<tr><td><code>kv.closed_timestamp.follower_reads_enabled</code></td><td>boolean</td><td><code>true</code></td><td>allow (all) replicas to serve consistent historical reads based on closed timestamp information</td></tr>
+<tr><td><code>kv.closed_timestamp.follower_reads_enabled</code></td><td>boolean</td><td><code>false</code></td><td>allow (all) replicas to serve consistent historical reads based on closed timestamp information</td></tr>
 <tr><td><code>kv.closed_timestamp.target_duration</code></td><td>duration</td><td><code>30s</code></td><td>if nonzero, attempt to provide closed timestamp notifications for timestamps trailing cluster time by approximately this duration</td></tr>
 <tr><td><code>kv.follower_read.target_multiple</code></td><td>float</td><td><code>3</code></td><td>if above 1, encourages the distsender to perform a read against the closest replica if a request is older than kv.closed_timestamp.target_duration * (1 + kv.closed_timestamp.close_fraction * this) less a clock uncertainty interval. This value also is used to create follower_timestamp(). (WARNING: may compromise cluster stability or correctness; do not edit without supervision)</td></tr>
 <tr><td><code>kv.import.batch_size</code></td><td>byte size</td><td><code>32 MiB</code></td><td>the maximum size of the payload in an AddSSTable request (WARNING: may compromise cluster stability or correctness; do not edit without supervision)</td></tr>

pkg/storage/replica_follower_read.go

@@ -32,7 +32,7 @@ import (
 var FollowerReadsEnabled = settings.RegisterBoolSetting(
 	"kv.closed_timestamp.follower_reads_enabled",
 	"allow (all) replicas to serve consistent historical reads based on closed timestamp information",
-	true,
+	false,
 )
 
 // canServeFollowerRead tests, when a range lease could not be