Replace double quotes when obfuscating SQL

InfluxDB escapes double quotes upon output which makes it a pain to deal
with. This ensures that if we're using PostgreSQL we don't store any
queries containing double quotes in InfluxDB, solving the escaping
problem.

lib/gitlab/metrics/obfuscated_sql.rb

@@ -30,9 +30,17 @@ module Gitlab
           regex = Regexp.union(regex, MYSQL_REPLACEMENTS)
         end
 
-        @sql.gsub(regex, '?').gsub(CONSECUTIVE) do |match|
+        sql = @sql.gsub(regex, '?').gsub(CONSECUTIVE) do |match|
           "#{match.count(',') + 1} values"
         end
+
+        # InfluxDB escapes double quotes upon output, so lets get rid of them
+        # whenever we can.
+        if Gitlab::Database.postgresql?
+          sql = sql.gsub('"', '')
+        end
+
+        sql
       end
     end
   end

spec/lib/gitlab/metrics/obfuscated_sql_spec.rb

@@ -75,5 +75,13 @@ describe Gitlab::Metrics::ObfuscatedSQL do
         expect(sql.to_s).to eq('SELECT x FROM y WHERE z IN (2 values)')
       end
     end
+
+    if Gitlab::Database.postgresql?
+      it 'replaces double quotes' do
+        sql = described_class.new('SELECT "x" FROM "y"')
+
+        expect(sql.to_s).to eq('SELECT x FROM y')
+      end
+    end
   end
 end