safari running slow even after emptying caches

Safari/Preferences/Advanced - enable the Develop menu, then go there and Empty Caches. Quit/reopen Safari and test. Then try Safari/History/Show History and delete all history items.  Quit/reopen Safari and test. You can also try try Safari/Clear History…. The down side is it clears all cookies. Doing this may cause some sites to no longer recognize your computer as one that has visited the web site. Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J.  When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder.  Select Library/Caches/com.apple.Safari/Cache.db and move it to the trash.

Go to Safari Preferences/Extensions and turn all extensions off. Quit/reopen Safari and test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.

 Safari Corruption       See post by Linc Davis

Boot to the Recovery Volume (command - R on a restart). Run Disk Utility and select First Aid. See if there are any errors. Reboot normally and test.

Go step by step and test.

    1. Restart the router

       Startup in Safe Mode and test.

       Launch Safari to test.

       Restart normally by clicking the “Restart” button at the bottom.

       Start up in Safe Mode. https://support.apple.com/en-us/HT201262

2. Delete Caches.db

    Back up your Mac.

    Close all windows and quit all applications. 

    Hold "option" key down and click "Go" menu in the Finder menu bar.

    Select "Library" from the dropdown.

    Library > Caches > com.apple.Safari > Caches.db

    Right click the Caches.db file and select "Move To Trash”.

    Close windows.

    Restart and relaunch Safari.

 3. Check for adware.

     Use  the latest release of Malwarebytes for Mac to remove malware/adware, if installed on your Mac.

     For instructions:  Install Malwarebytes for Mac          Uninstall Malwarebytes for Mac

     Click the “Scan Now” button. Once done, quit Malwarebytes for Mac.

     Restart the computer and relaunch Safari holding the shift key down.

 4  Download EtreCheck, https://etrecheck.com/maspro  and post the report here.

      Click  “Click to download” button,

      Open Downloads folder, click on it to open, and then select ”Open”.

      “Choose a problem” from the popup menu box, and then “Start EtreCheck” in the dialog.

      Click “Share Report” button in the toolbar, select “Copy report” .

      Paste the report when you reply.

      Note

      This is a diagnostic test.

      If 5000 words limit applies:

      Split the report into two parts and post as two separate posts. 

There is a workaround.

    Download Safari Technology Preview and test.

    Safari Technology Preview is a self standing developer version of Safari with some advanced features and latest bug fixes.

    Bookmarks will be automatically imported.

    After testing, you can remove it from Applications folder if you wish. 

I often run both versions of Safari concurrently.

    https://developer.apple.com/safari/technology-preview/

If nothing works, reinstalling macOS is an option.

How to reinstall macOS from macOS Recovery - Apple Support

Please don't forget to backup your Mac before reinstalling macOS.

Create a new user in Users & Groups located in System Preferences. Be certain it is an Administrator Account. See if this occurs in that account. If it does, then it pertains only to the current account you are using. If not, then it pertains, to the whole Mac.

Reinstalling the Operating System should fix any bugs in Safari, as intended.

Do not reformat the drive; just reinstall the operating system.

Contact Apple Support on this reinstallation (800)MY-APPLE

If you are using AdBlock, uninstall it.

AdBlock has problem with macOS Mojave.

https://help.getadblock.com/support/solutions/articles/6000055763-how-do-i-install-adblock-how-do-i-uninstall-adblock-

https://help.getadblock.com/support/solutions/articles/6000198750#uninstall

Uninstall Adobe Flash Player.

If you really need it, reinstall it.

Adobe Flash Player plug-in uninstall    https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html

Adobe Flash Player plug-in  install       https://get.adobe.com/flashplayer/

From the EtreCheck report:

Safari Extensions:

AdBlock.safariextz - BetaFish, Inc. - https://getadblock.com (installed 2018-10-04)

May be that macOS Mojave moved it to the Extensions Folder.

Hold the Option key down and click "Go" menu in the Finder menubar.

Choose Library from the dropdown.

Scroll down and click open the Safari folder.

Scroll down and click open the Extensions folder

Do you see AdBlock there?

Library > Safari > Extensions > AdBlock.

Safari version 12 /macOS Mojave won't have the Caches.db file showing.

It is put in Container and kept away.

Run EtreCheck and see what it says.

Repairing Disk/First Aid from macOS Recovery is another option.

Mozilla Firefox or Google Chrome: Use those for alternative uses of Web browsers.

How far are you from your router? If it’s your own router, plug it directly into it and see where that takes you in terms of connections. And of your router is slow (i.e. AC300), and there is lots of streaming taking place(Gaming and AppleTV), consider upgrading your router.

Else-wise, contact the network administrator, as they would know about how to configure all of this.

If it’s hardware, it’s hardware. Using an alternative network adapter could be another choice.

Do you have any anti-virus software or cleaner application running?

It may not help, but try running/posting the Etrecheck report. Use PasteBin for the report.

EDIT:

Talk the the network administrator, they would be the one(s) with optimum ability to fix this.

Force Quit Safari from Activity Monitor.

Back to your user account, try Safari.

Tough it gave problem, what happens if you empty caches from Develop menu again.

It may be stuck while emptying caches.

I usually empty caches twice.

This will also empty network caches, and favicon caches.

It may not help, but try running/posting the Etrecheck report. If the log won’t post, try posting it in Pastebin and provide a link in a reply        Pastebin

Open Activity Monitor and quit Safari.

See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support