fix(postgres): close socket actively when timeout happens during query (

#11480)

Currently, we do set/keep socket keepalive after every Postgres SQL query, based on keepalive timeout configured or lua_socket_keepalive_timeout(default 60s).
This could go wrong under some cases, when a query encounters read timeout when trying to receive data from a database with high load, the query ends on Kong's side but the query result may be sent back after timeout happens, and the result data will be lingering inside the socket buffer, and the socket itself get reused for subsequent query, then the subsequent query might get the incorrect result from the previous query.

The PR checks the query result's err string, and if any error happens, it'll try to close the socket actively so that the subsequent query will establish new clean ones.

Fix FTI-5322

(cherry picked from commit d2da4db)

CHANGELOG/unreleased/kong/11480.yaml

@@ -0,0 +1,7 @@
+message: Fix a problem that abnormal socket connection will be reused when querying Postgres database.
+type: bugfix
+scope: Core
+prs:
+  - 11480
+jiras:
+  - "FTI-5322"

kong/db/strategies/postgres/connector.lua

@@ -502,6 +502,7 @@ function _mt:query(sql, operation)
     operation = "write"
   end
 
+  local conn, is_new_conn
   local res, err, partial, num_queries
 
   local ok
@@ -510,23 +511,36 @@ function _mt:query(sql, operation)
     return nil, "error acquiring query semaphore: " .. err
   end
 
-  local conn = self:get_stored_connection(operation)
-  if conn then
-    res, err, partial, num_queries = conn:query(sql)
-
-  else
-    local connection
+  conn = self:get_stored_connection(operation)
+  if not conn then
     local config = operation == "write" and self.config or self.config_ro
 
-    connection, err = connect(config)
-    if not connection then
+    conn, err = connect(config)
+    if not conn then
       self:release_query_semaphore_resource(operation)
       return nil, err
     end
+    is_new_conn = true
+  end
+
+  res, err, partial, num_queries = conn:query(sql)
 
-    res, err, partial, num_queries = connection:query(sql)
+  -- if err is string then either it is a SQL error
+  -- or it is a socket error, here we abort connections
+  -- that encounter errors instead of reusing them, for
+  -- safety reason
+  if err and type(err) == "string" then
+    ngx.log(ngx.DEBUG, "SQL query throw error: ", err, ", close connection")
+    local _, err = conn:disconnect()
+    if err then
+      -- We're at the end of the query - just logging if
+      -- we cannot cleanup the connection
+      ngx.log(ngx.ERR, "failed to disconnect: ", err)
+    end
+    self.store_connection(nil, operation)
 
-    setkeepalive(connection)
+  elseif is_new_conn then
+    setkeepalive(conn)
   end
 
   self:release_query_semaphore_resource(operation)

spec/02-integration/03-db/01-db_spec.lua

@@ -450,6 +450,50 @@ for _, strategy in helpers.each_strategy() do
     end)
   end)
 
+  describe("#testme :query() [#" .. strategy .. "]", function()
+    lazy_setup(function()
+      helpers.get_db_utils(strategy, {})
+    end)
+
+    postgres_only("establish new connection when error occurred", function()
+      ngx.IS_CLI = false
+
+      local conf = utils.deep_copy(helpers.test_conf)
+      conf.pg_ro_host = conf.pg_host
+      conf.pg_ro_user = conf.pg_user
+
+      local db, err = DB.new(conf, strategy)
+
+      assert.is_nil(err)
+      assert.is_table(db)
+      assert(db:init_connector())
+      assert(db:connect())
+
+      local res, err = db.connector:query("SELECT now();")
+      assert.not_nil(res)
+      assert.is_nil(err)
+
+      local old_conn = db.connector:get_stored_connection("write")
+      assert.not_nil(old_conn)
+
+      local res, err = db.connector:query("SELECT * FROM not_exist_table;")
+      assert.is_nil(res)
+      assert.not_nil(err)
+
+      local new_conn = db.connector:get_stored_connection("write")
+      assert.is_nil(new_conn)
+
+      local res, err = db.connector:query("SELECT now();")
+      assert.not_nil(res)
+      assert.is_nil(err)
+
+      local res, err = db.connector:query("SELECT now();")
+      assert.not_nil(res)
+      assert.is_nil(err)
+
+      assert(db:close())
+    end)
+  end)
 
   describe(":setkeepalive() [#" .. strategy .. "]", function()
     lazy_setup(function()