The webmasters are often troubled by junk comments. Website spam attacks can paralyze a website, impact normal operations, and reduce the user experience. Although I installed Akismet , this plugin does not prevent spammers from inserting into the database, so it is not so ideal.
I found a WordPress spam protection plugin called WP SpamShield, I checked introduction, found WP-SpamShield is a suitable wordpress spam protection plugin.
WP-SpamShield is All-in-One Anti-Spam Plugin for WordPress – Without CAPTCHAs, There are two layers of leading edge anti-spam protection that work together to block both automated (spambots) and human spam; No More Wasted Time Sifting Through the Comment Spam Queue, Not allowing spam into the database improves security by potentially preventing SQL injection, DDoS, and XSS exploit attacks through automated spam comment submissions.