WordPress致命错误：在1832行的wp-includes / wp-db.php中,允许的内存大小为536870912字节(试图分配77个字节)

我最近在我的WordPress网站上发现我有时会遇到500内部服务器错误.我检查了日志,我有很多行,如：

[Mon Oct 03 01:25:24.357439 2016] [fcgid:warn] [pid 12840] [client
83.27.211.107:36968] mod_fcgid: stderr: PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 77 bytes)
in /var/www/vhosts/mywebsite/public_html/wp-includes/wp-db.PHP on line
1832

我试图增加内存限制：

define( ‘WP_MAX_MEMORY_LIMIT’ , ‘512M’ );

define( ‘WP_MEMORY_LIMIT’ , ‘512M’ );

甚至更多,但它没有奏效.无论我设置它仍然超过内存限制一些字节.我认为对数据库的一些查询存在问题,但是如何检查哪个？

includes / wp-db.PHP的内容：

} else {
    $num_rows = 0;
    if ( $this->use_MysqLi && $this->result instanceof MysqLi_result ) {
        while ( $row = MysqLi_fetch_object( $this->result ) ) {
            $this->last_result[$num_rows] = $row;
            $num_rows++;
        }
    } elseif ( is_resource( $this->result ) ) {
        // server crashing at line below
        while ( $row = MysqL_fetch_object( $this->result ) ) {
            $this->last_result[$num_rows] = $row;
            $num_rows++;
        }
    }

    // Log number of rows the query returned
    // and return number of rows selected
    $this->num_rows = $num_rows;
    $return_val     = $num_rows;
}

解决方法:

问题是由iThemes Security插件引起的.我关掉它,错误消失了.如果我知道这个插件的哪个部分导致超出内存限制,我会更多地研究这个问题并编辑这个答案.