index does not release memory

[parihaaraka]

Tarantool 2.6.2-0-g34d504d7d

do
    local s = box.schema.space.create('test', {format = {{'id', 'unsigned'}}, temporary = true})
    local pk = s:create_index('pk', {parts = {'id'}})
    -- peak load
    for i = 1, 500000 do
        s:insert({i})
    end
    -- wipe outdated records after some time
    for i = 1, 499000 do
        s:delete(i)
    end

    local res = string.format('space size: %d kb, index size: %d kb',
        tonumber(s:bsize() / 1024),
        tonumber(pk:bsize() / 1024)
    )
    s:drop()
    return res
end

space size: 5 kb, index size: 11040 kb

[Korablev77]

It's not a bug. See #4780

I would say it's not a bug but known behavior. Any index does not free any memory; it stays reserved for further insertions. This approach not only makes implementation easier but have some performance advantages as well. I'm not sure we'll change it anytime soon.

Probably we should document this behaviour.

[parihaaraka]

..and propose some kind of index:vacuum()