From c5e4485d3d658b5fc53c2e254e93338ae4348c13 Mon Sep 17 00:00:00 2001
From: Ayrat Badykov <ayratin555@gmail.com>
Date: Fri, 23 Aug 2019 12:54:27 +0300
Subject: [PATCH 1/4] deduplicate coin history records by delta

On coin history page we show records that are found
in the db. Since we may fetch a lot of duplicated balances
for the same address if its balance is not changes for
multiple blocks.

This PR adds deduplication by delta value to remove duplication.
---
 apps/explorer/lib/explorer/chain.ex        |  3 +++
 apps/explorer/test/explorer/chain_test.exs | 26 ++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/apps/explorer/lib/explorer/chain.ex b/apps/explorer/lib/explorer/chain.ex
index 58253c0f27..a6200a81f9 100644
--- a/apps/explorer/lib/explorer/chain.ex
+++ b/apps/explorer/lib/explorer/chain.ex
@@ -2967,6 +2967,9 @@ defmodule Explorer.Chain do
     |> CoinBalance.fetch_coin_balances(paging_options)
     |> page_coin_balances(paging_options)
     |> Repo.all()
+    |> Enum.dedup_by(fn record ->
+      record.delta == Decimal.new(0)
+    end)
   end
 
   def get_coin_balance(address_hash, block_number) do
diff --git a/apps/explorer/test/explorer/chain_test.exs b/apps/explorer/test/explorer/chain_test.exs
index f49be6da4e..10788b60ba 100644
--- a/apps/explorer/test/explorer/chain_test.exs
+++ b/apps/explorer/test/explorer/chain_test.exs
@@ -4159,4 +4159,30 @@ defmodule Explorer.ChainTest do
       assert Chain.staking_pools_count(:inactive) == 1
     end
   end
+
+  describe "address_to_coin_balances/2" do
+    test "deduplicates records by zero delta" do
+      address = insert(:address)
+
+      1..5
+      |> Enum.each(fn block_number ->
+        insert(:block, number: block_number)
+        insert(:fetched_balance, value: 1, block_number: block_number, address_hash: address.hash)
+      end)
+
+      insert(:block, number: 6)
+      insert(:fetched_balance, value: 2, block_number: 6, address_hash: address.hash)
+
+      assert [first, second, third] = Chain.address_to_coin_balances(address.hash, [])
+
+      assert first.block_number == 6
+      assert first.delta == Decimal.new(1)
+
+      assert second.block_number == 5
+      assert second.delta == Decimal.new(0)
+
+      assert third.block_number == 1
+      assert third.delta == Decimal.new(1)
+    end
+  end
 end

From e8ba3b22785931c890ebc856096b99482c99a399 Mon Sep 17 00:00:00 2001
From: Ayrat Badykov <ayratin555@gmail.com>
Date: Fri, 23 Aug 2019 12:59:07 +0300
Subject: [PATCH 2/4] add CHANGELOG entry

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0c26c016be..d6cfce7118 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - [#2497](https://github.com/poanetwork/blockscout/pull/2497) - Add generic Ordered Cache behaviour and implementation
 
 ### Fixes
+- [#2616](https://github.com/poanetwork/blockscout/pull/2616) - deduplicate coin history records by delta
 - [#2592](https://github.com/poanetwork/blockscout/pull/2592) - process new metadata format for whisper
 - [#2572](https://github.com/poanetwork/blockscout/pull/2572) - Ease non-critical css
 - [#2570](https://github.com/poanetwork/blockscout/pull/2570) - Network icons preload

From 045652a505a93120d28a1db92fc20241a6a8dd40 Mon Sep 17 00:00:00 2001
From: Ayrat Badykov <ayratin555@gmail.com>
Date: Fri, 23 Aug 2019 14:00:16 +0300
Subject: [PATCH 3/4] fix tests

---
 apps/explorer/lib/explorer/chain.ex | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/apps/explorer/lib/explorer/chain.ex b/apps/explorer/lib/explorer/chain.ex
index a6200a81f9..c781a3463e 100644
--- a/apps/explorer/lib/explorer/chain.ex
+++ b/apps/explorer/lib/explorer/chain.ex
@@ -2968,7 +2968,11 @@ defmodule Explorer.Chain do
     |> page_coin_balances(paging_options)
     |> Repo.all()
     |> Enum.dedup_by(fn record ->
-      record.delta == Decimal.new(0)
+      if record.delta == Decimal.new(0) do
+        :dup
+      else
+        System.unique_integer
+      end
     end)
   end
 

From cd979c02c2f257fa06eb79d05684cd14333e6406 Mon Sep 17 00:00:00 2001
From: Ayrat Badykov <ayratin555@gmail.com>
Date: Fri, 23 Aug 2019 14:02:46 +0300
Subject: [PATCH 4/4] mix format

---
 apps/explorer/lib/explorer/chain.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/apps/explorer/lib/explorer/chain.ex b/apps/explorer/lib/explorer/chain.ex
index c781a3463e..b2c18e8a50 100644
--- a/apps/explorer/lib/explorer/chain.ex
+++ b/apps/explorer/lib/explorer/chain.ex
@@ -2971,7 +2971,7 @@ defmodule Explorer.Chain do
       if record.delta == Decimal.new(0) do
         :dup
       else
-        System.unique_integer
+        System.unique_integer()
       end
     end)
   end