server: Speed up the statistics computation from the database

server/app/com/xsn/explorer/data/anorm/dao/StatisticsPostgresDAO.scala

@@ -13,16 +13,15 @@ class StatisticsPostgresDAO {
   def getStatistics(implicit conn: Connection): Statistics = {
     val result = SQL(
       s"""
-        |SELECT
-        |  (
-        |    SELECT SUM(received - spent) FROM balances
-        |    WHERE address <> '$BurnAddress'
+        |SELECT (
+        |    (SELECT value FROM aggregated_amounts WHERE name = 'available_coins') -
+        |    (SELECT COALESCE(SUM(received - spent), 0) FROM balances WHERE address = '$BurnAddress')
         |  ) AS total_supply,
         |  (
-        |    SELECT SUM(received - spent) FROM balances
-        |    WHERE address NOT IN (SELECT address FROM hidden_addresses)
+        |    (SELECT value FROM aggregated_amounts WHERE name = 'available_coins') -
+        |    (SELECT COALESCE(SUM(received - spent), 0) FROM balances WHERE address IN (SELECT address FROM hidden_addresses))
         |  ) AS circulating_supply,
-        |  (SELECT COUNT(*) FROM transactions) AS transactions,
+        |  (SELECT n_live_tup FROM pg_stat_all_tables WHERE relname = 'transactions') AS transactions,
         |  (SELECT COALESCE(MAX(height), 0) FROM blocks) AS blocks
       """.stripMargin
     ).as(StatisticsParsers.parseStatistics.single)

server/test/com/xsn/explorer/data/StatisticsPostgresDataHandlerSpec.scala

@@ -6,6 +6,7 @@ import com.xsn.explorer.data.anorm.{BalancePostgresDataHandler, StatisticsPostgr
 import com.xsn.explorer.data.common.PostgresDataHandlerSpec
 import com.xsn.explorer.helpers.DataHelper
 import com.xsn.explorer.models.{Address, Balance}
+import org.scalatest.OptionValues._
 
 class StatisticsPostgresDataHandlerSpec extends PostgresDataHandlerSpec {
 
@@ -20,7 +21,7 @@ class StatisticsPostgresDataHandlerSpec extends PostgresDataHandlerSpec {
 
     "exclude hidden_addresses from the circulating supply" in {
       val hiddenAddress = DataHelper.createAddress("XfAATXtkRgCdMTrj2fxHvLsKLLmqAjhEAt")
-      val circulatingSupply = dataHandler.getStatistics().get.circulatingSupply
+      val circulatingSupply = dataHandler.getStatistics().get.circulatingSupply.getOrElse(0)
 
       database.withConnection { implicit conn =>
         _root_.anorm.SQL(
@@ -35,19 +36,19 @@ class StatisticsPostgresDataHandlerSpec extends PostgresDataHandlerSpec {
       balanceDataHandler.upsert(balance).isGood mustEqual true
 
       val result = dataHandler.getStatistics().get
-      result.circulatingSupply mustEqual circulatingSupply
+      result.circulatingSupply.value mustEqual circulatingSupply
     }
 
     "exclude the burn address from the total supply" in {
       val burnAddress = Address.from(StatisticsPostgresDAO.BurnAddress).get
 
-      val totalSupply = dataHandler.getStatistics().get.totalSupply
+      val totalSupply = dataHandler.getStatistics().get.totalSupply.getOrElse(0)
 
       val balance = Balance(burnAddress, received = BigDecimal(1000), spent = BigDecimal(500))
       balanceDataHandler.upsert(balance).isGood mustEqual true
 
       val result = dataHandler.getStatistics().get
-      result.totalSupply mustEqual totalSupply
+      result.totalSupply.value mustEqual totalSupply
     }
   }
 }