How can one remove lag spikes due to memory dumps?

Possible solution:

OptiFine

You can download OptiFine here.

OptiFine is a great way of getting rid of lagg spikes, and has a lot of settings to adjust, and could possibly remove your lagg spikes, try to put everything off, or as low as possible, or just adjust it to your likings, also if you go to the setting called Other... you should see an option called Autosave, put it on 30m and it should happen less frequently.

Allocating more RAM to Minecraft

This one depends on the amount of RAM you have available, the more RAM you have, the better it runs, as Minecraft uses quite a lot of it, and allowing it to use more can make it run smoother.

Start the Minecraft Launcher and then go to Edit Profile. You should now see all the way down an option called JVM Arguments, enable it, and write the following: -Xmx2G -Xmn128M. If -Xmx or -Xmn is already in there, remove those. What this will do is allow Minecraft to allocate up to 2GB RAM to your Minecraft when you start it up, and it will always run with at least 128MB.

Of course this depends on how much RAM you have, if you only have 2GB RAM on your PC/Laptop then I strongly suggest you run it with -Xmx1G -Xmn64M And if you have more, I suggest you locate at least half of the RAM you have. Make sure that you don't locate all of your RAM to Minecraft, or other applications might not work anymore or freeze, they might even crash.

Note that in order to allocate more than 1.8G of RAM to Minecraft (or any java program) you require a 64-bit computer with 64-bit java. (The minimalist JRE that the more recent Windows versions of Minecraft install automatically will be 64 bit if your system supports it.)

Turn off all/some of your applications

When playing Minecraft, I strongly suggest you turn off most of, or all of your applications so it will run as smoothly as possible, because Minecraft isn't the only program that eats your RAM.

Increasing process priority

I recommend not doing this, but if your computer is really that bad, and you know what you're doing then you should continue reading this option.

When you're in your Task Manager, on Windows 8(.1) you should see all of your applications currently running, click on More details and then when you located Minecraft, right click it, and hover over to the option Go to details or something similar looking like that, and you should now see the java process highlighted, right click it, and hover over Priority or something similar looking, and click on the second highest option, as Realtime could crash your PC/Laptop or whatever OS you are using, you should be good to go now!

Note: The priority option could bring issues like some programs not responding/freezing so I recommend to keep Task Manager open to change this at anytime.

I think it because of mods?, Because last time I use Minecraft with mods it doesn't lag,

Mods List: Optifine Just Enough Item Grappling Hook Mod

That's the Java garbage collector. You can add the following launch options:

-XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1

That should decrease the garbage collection lag dramatically by parallelizing garbage collection and decreasing the quantity and effect of collection events.

(taken from https://aikar.co/2018/07/02/tuning-the-jvm-g1gc-garbage-collector-flags-for-minecraft/)

You can also try running the latest 64-bit version of Java - newer versions of Minecraft now support Java 11+!

Finally, as the other responses said, Optifine (turn on the all options under Video Settings > Performance and increase the framerate to Unlimited) and performance enhancing mods (BetterFPS, FoamFix, Sodium/Phosphor/Lithium, etc.) can help a lot.