Thanks. 

I bumped wait_timeout to 180, then 360.  No change.

After reading more stackoverflow, I added similar connect_timeout and interactive_timeout values to amysqli.php, so i ended up looking like this:

      $connection->query("SET session connect_timeout=720;");
      $connection->query("SET session wait_timeout=720;");
      $connection->query("SET session interactive_timeout=720;");

Stackoverflow also led me to make more changes to php.ini.

I already had these settings:
max_execution_time=18000
max_input_time - 1200
memory_limit - 512M

I made these changes:
Uncomment two lines and increase values:
realpath_cache_size = 128k
realpath_cache_ttl = 1800
(I have no idea why these were commented out, but they never interfered with prior dev or backup of other CMS sites.)

Also:
default_socket_timeout=300
mysql.connect_timeout=300 -- on line 1199
mysql.connect_timeout=300 -- on line 2062
I don't know why there are two instances of the latter element.

I rebooted the virtual server and ran a backup.  It successfully finished all 3 steps in approx 3 minutes. 

Comments;
1 - The large time values, mem_limits and cache-sizes above are all recent changes I implemented after reading about how to make Abantecart run seamlessly.  Prior to my recent AC adventure, I never paid any attention to any of these values other than execution_time and memory_limit, and those two values were set much lower than what is recommended for AC.  So, if you have prior experience with other CMS apps, and are new to AC, you should anticipate making some changes like those described above. 

2 - The backup finished very quickly.  This suggests that the new amysqli timeouts or the uncommented caches or the slightly expanded php.ini timeouts were the solution.  I plan to reduce some of the values above back towards more conventional values. 

Thanks. 

Thanks for the reply. 

From the perspective of a new AbanteCart user: 
1 - The most efficient way to set up new products is to clone a similar product. 
2 - The clone feature is a time-saving and useful feature.
3 - The clone feature has an unexpected side effect: when it is used to clone a product that has a custom layout, it will add an un-needed Layout Copy to the roster of layouts.
4 - This will rapidly lead to a very long list of unnecessary Layout Clones, esp for large stores.

When a user encounters an unexpected outcome, it is not uncommon for that user to ask whether the outcome should have occurred.  I did that above.  It's easy to see that an ever-expanding list of Layout Clones is not a desirable side effect of an otherwise useful product setup feature. 

Sometimes this process can help identify a problem that has a reasonable probability of recurring with other users. 

I have one remaining question.  I would be great to get an answer...

After going back and reassigning a single layout to my products, is there a way to delete all the Layout Clones that I inadvertently created while using the Product Clone feature, so that my Layout list is not clogged with a large number of unneeded layout clones?

Thanks. 

Yes,
It automatically generates all image when users click on images and user go to that pages.
However, I read AbanteCart and follow Official Nginx configure both in Github and in application files (nginx.conf.txt) I configure in abantecard.conf But it does not yet work on my website when I go to website  >jersey-cotton-striped-polo-shirt it back to home page.

Server logs.

2017/06/23 11:27:04 [error] 981#0: *192 open() "/home/saku/abantecard/public_html404" failed (2: No such file or directory), client: 103.197.107.248, server: akhura.com, request: "GET /mens-fine-cotton-giraffe-polo-shirtsindex.php?rt=r/extension/banner_manager&type=1&banner_id=15&_=1498217225433 HTTP/1.1", host: "akhura.com", referrer: "akhura.com/mens-fine-cotton-giraffe-polo-shirts"


This is my configuration

server {

    listen ..;

    root ......public_html;
    index index.php index.html;

    server_name.

#   access_log ......akhura_access.log;
    error_log  ......errors.log;

    autoindex off;
    proxy_connect_timeout 100s;
    proxy_read_timeout 100s;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }
  location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
    }

 location ~* \.(engine|inc|info|install|make|module|profile|test|po|sh|.*sql|theme|tpl(\.php)?|xtmpl)$|^(\..*|Entries.*|Repository|Root|Tag|Template)$|\.php_ {
        deny all;

    }

  location ~ /\. {
        deny all;
        access_log off;
        log_not_found off;
    }

 location ~* ^(.*)\.(jpg|png|gif)$ {

   set $hidpi_uri $1@2x.png;
        if ($http_cookie !~ 'HTTP_IS_RETINA=1') {
          break;
        }
        try_files $hidpi_uri $uri =404;
    }

 location ~*  \.(jpg|jpeg|png|gif|css|js|ico)$ {
        expires max;
        log_not_found off;
    }

    location ~ /(system/logs|resources/download) {
      deny all;
      return 403;
    }

    location ~ \.php$ {

        try_files $uri = 404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass unix:var/run/php/php7.0-fpm-saku.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
    }
}

Hello.

I think best way to get support with 3rd party templates is contact developer 
https://marketplace.abantecart.com/order-support

it generates on every request or only on first visit of page?