Need a method remove all keys but keep the file size not changed

[calvin2021y]

This is not a bug report but a future request.

I need a method to remove all keys, but not trim and truncate file size to DEFAULT_MMAP_SIZE.

any suggestions how to do it myself, or MMKV will consider add this future?

[calvin2021y]

I need reuse the db instance without close it. keep the file size to reduce the IO overhead.

[lingol]

What do you mean by saying reduce IO overhead? Do you find MMKV's space expansion algorithm not working for you?

[calvin2021y]

The file size reduced into 4KB after clear.

I use 2 MMKV instance as log rotate at high speed, after one full then change to other one.

In this case every time rotate the file size changed, I guess keep the file size not change but destroy the data inside it will avoid a lot system call and block time.

[lingol]

Why do you need two instances and rotate them? It's quite a strange usage.

[calvin2021y]

1. avoid thread lock, the log always read/write in one thread

2. if I need destroy one, no need search by key range

3. when need backup or send to remote, just move the task into other thread.

[lingol]

I take it that you have set a size limit or key count limit per instance. How large is one file grow to, normally speaking?

[calvin2021y]

Yes, I use count limit. the file size could be 10M to 100M depend the logs item size and MAX_LOG_ENTRY_LIMIT(adjustable).

[kaitian521]

Same feature is needed for me.

A faster clearAll() is somehow like clearMemoryCache, but do not call doCleanMemoryCache in m_file.

In another word, it will not do any system IO calls for better performance.

If some groups of keys are inserted into MMKV together every time, we can first call clearAllFast, then put them from start of file: it will not expand, will not trim, just keep it origin size which is expected.