diff --git a/sstables/row.cc b/sstables/row.cc
index e67efcd17a..8fcc378992 100644
--- a/sstables/row.cc
+++ b/sstables/row.cc
@@ -532,8 +532,9 @@ future<> data_consume_context::read() {
 
 data_consume_context sstable::data_consume_rows(
         row_consumer& consumer, uint64_t start, uint64_t end) {
+    auto estimated_size = std::min(uint64_t(sstable_buffer_size), align_up(end - start, uint64_t(8 << 10)));
     return std::make_unique<data_consume_context::impl>(
-            consumer, data_stream_at(start), end - start);
+            consumer, data_stream_at(start, estimated_size), end - start);
 }
 
 data_consume_context sstable::data_consume_rows(row_consumer& consumer) {
diff --git a/sstables/sstables.cc b/sstables/sstables.cc
index 8713239c8a..59a33c0f21 100644
--- a/sstables/sstables.cc
+++ b/sstables/sstables.cc
@@ -21,6 +21,7 @@
 #include "unimplemented.hh"
 #include <boost/algorithm/string.hpp>
 #include <regex>
+#include <core/align.hh>
 
 namespace sstables {
 
@@ -752,14 +753,23 @@ future<index_list> sstable::read_indexes(uint64_t summary_idx) {
     uint64_t position = _summary.entries[summary_idx].position;
     uint64_t quantity = _summary.header.sampling_level;
 
+    uint64_t estimated_size;
+    if (++summary_idx >= _summary.header.size) {
+        estimated_size = index_size() - position;
+    } else {
+        estimated_size = _summary.entries[summary_idx].position - position;
+    }
+
+    estimated_size = std::min(uint64_t(sstable_buffer_size), align_up(estimated_size, uint64_t(8 << 10)));
+
     struct reader {
         uint64_t count = 0;
         std::vector<index_entry> indexes;
         shared_file_random_access_reader stream;
-        reader(file f, uint64_t quantity) : stream(f) { indexes.reserve(quantity); }
+        reader(file f, uint64_t quantity, uint64_t estimated_size) : stream(f, estimated_size) { indexes.reserve(quantity); }
     };
 
-    auto r = make_lw_shared<reader>(_index_file, quantity);
+    auto r = make_lw_shared<reader>(_index_file, quantity, estimated_size);
 
     r->stream.seek(position);
 
@@ -1470,12 +1480,12 @@ sstable::component_type sstable::component_from_sstring(sstring &s) {
     return reverse_map(s, _component_map);
 }
 
-input_stream<char> sstable::data_stream_at(uint64_t pos) {
+input_stream<char> sstable::data_stream_at(uint64_t pos, uint64_t buf_size) {
     if (_compression) {
         return make_compressed_file_input_stream(
                 _data_file, &_compression, pos);
     } else {
-        return make_file_input_stream(_data_file, pos);
+        return make_file_input_stream(_data_file, pos, buf_size);
     }
 }
 
diff --git a/sstables/sstables.hh b/sstables/sstables.hh
index 27e4b96d86..69e53068cd 100644
--- a/sstables/sstables.hh
+++ b/sstables/sstables.hh
@@ -334,7 +334,7 @@ private:
 
     future<index_list> read_indexes(uint64_t summary_idx);
 
-    input_stream<char> data_stream_at(uint64_t pos);
+    input_stream<char> data_stream_at(uint64_t pos, uint64_t buf_size = 8192);
 
     // Read exactly the specific byte range from the data file (after
     // uncompression, if the file is compressed). This can be used to read