db: handle truncation of shared files with no points

Previously, our iterator creation code created invalid iterators
instead of returning nil for point iterators if we tried to create
point iterators on a file with `hasPointKeys == false`. This change
addresses that, and also updates `truncateSharedFile` to handle
cases where the point key iterator is nil.

Fixes cockroachdb#3761.

scan_internal.go

@@ -559,7 +559,10 @@ func (d *DB) truncateSharedFile(
 	if needsLowerTruncate {
 		sst.SmallestPointKey.UserKey = sst.SmallestPointKey.UserKey[:0]
 		sst.SmallestPointKey.Trailer = 0
-		kv := iter.SeekGE(lower, base.SeekGEFlagsNone)
+		var kv *base.InternalKV
+		if iter != nil {
+			kv = iter.SeekGE(lower, base.SeekGEFlagsNone)
+		}
 		foundPointKey := kv != nil
 		if kv != nil {
 			sst.SmallestPointKey.CopyFrom(kv.K)
@@ -598,7 +601,10 @@ func (d *DB) truncateSharedFile(
 	if needsUpperTruncate {
 		sst.LargestPointKey.UserKey = sst.LargestPointKey.UserKey[:0]
 		sst.LargestPointKey.Trailer = 0
-		kv := iter.SeekLT(upper, base.SeekLTFlagsNone)
+		var kv *base.InternalKV
+		if iter != nil {
+			kv = iter.SeekLT(upper, base.SeekLTFlagsNone)
+		}
 		foundPointKey := kv != nil
 		if kv != nil {
 			sst.LargestPointKey.CopyFrom(kv.K)

table_cache.go

@@ -485,7 +485,7 @@ func (c *tableCacheShard) newIters(
 	if kinds.RangeDeletion() && file.HasPointKeys && err == nil {
 		iters.rangeDeletion, err = c.newRangeDelIter(ctx, file, cr, dbOpts)
 	}
-	if kinds.Point() && err == nil {
+	if kinds.Point() && file.HasPointKeys && err == nil {
 		iters.point, err = c.newPointIter(ctx, v, file, cr, opts, internalOpts, dbOpts)
 	}
 	if err != nil {

testdata/ingest_shared

@@ -1307,3 +1307,53 @@ next
 ----
 .
 .
+
+# Regression test for #3761. Replicate an sstable
+# which does not have point keys.
+
+reset
+----
+
+switch 2
+----
+ok
+
+batch
+range-key-set a c @4 value
+----
+
+flush
+----
+
+compact a-z
+----
+ok
+
+lsm
+----
+L6:
+  000005:[a#10,RANGEKEYSET-c#inf,RANGEKEYSET]
+
+switch 1
+----
+ok
+
+replicate 2 1 a z
+----
+replicated 1 shared SSTs
+
+lsm
+----
+L6:
+  000005(000005):[a#11,RANGEKEYSET-c#inf,RANGEKEYDEL]
+
+iter
+first
+next
+next
+next
+----
+a: (., [a-c) @4=value UPDATED)
+.
+.
+.