coc#pum#next feels laggy

[xR3b0rn]

Hey there,

I'm coming from Neovim's native LSP client. When using the nvim-cmp plugin there, I can scroll through completion suggestions very quickly by holding down .

When I try the same with coc-clangd, the scrolling feels extremely laggy - I can barely see any movement in the currently selected suggestion.

I understand that CoC uses a different architecture, and that some delay is expected due to the extra step of communicating with the CoC server. I just want to confirm whether this is expected behavior, or if I might have something misconfigured on my end.

Thanks in advance! 🙏

PS. this is my coc.lua:

return {
  "neoclide/coc.nvim",
  branch = "release",
  lazy = false,
  keys = {
    -- Normal mode keymaps for CoC actions
    { "gD",          "<Plug>(coc-declaration)",             desc = "Goto declaration",      mode = "n" },
    { "gd",          "<Plug>(coc-definition)",              desc = "Goto definition",       mode = "n" },
    { "K",           ":call CocActionAsync('doHover')<CR>", desc = "Hover",                 mode = "n" },
    { "<leader>vws", ":CocList -I symbols<CR>",             desc = "Workspace symbol",      mode = "n" },
    { "<leader>vd",  ":CocDiagnostics<CR>",                 desc = "Open diagnostics list", mode = "n" },
    { "[d",          "<Plug>(coc-diagnostic-prev)",         desc = "Prev diagnostic",       mode = "n" },
    { "]d",          "<Plug>(coc-diagnostic-next)",         desc = "Next diagnostic",       mode = "n" },
    { "<leader>vca", "<Plug>(coc-codeaction)",              desc = "Code action",           mode = "n" },
    { "<leader>vrr", "<Plug>(coc-references)",              desc = "List references",       mode = "n" },
    { "<leader>vrn", "<Plug>(coc-rename)",                  desc = "Rename symbol",         mode = "n" },
    { "<c-f>",       "<Plug>(coc-format)",                  desc = "Format file",           mode = "n" },
    { "<C-n>",       'coc#pum#next(0)',                     desc = "Next completion item",  mode = "i", expr = true, silent = true },
    { "<C-p>",       'coc#pum#prev(0)',                     desc = "Prev completion item",  mode = "i", expr = true, silent = true },
    { "<C-y>",       'coc#pum#confirm()',                   desc = "Confirm completion",    mode = "i", expr = true, silent = true },
    { "<C-Space>",   'coc#refresh()',                       desc = "Trigger completion",    mode = "i", expr = true, silent = true },
  },
}

[fannheyward]

What's your :CocInfo?

[xR3b0rn]

## versions

vim version: NVIM v0.11.2
node version: v18.19.1
coc.nvim version: 0.0.82-b0a699d 2025-09-22 17:34:21 +0800
coc.nvim directory: /home/primes/.local/share/nvim/lazy/coc.nvim
term: tmux
platform: linux

## Log of coc.nvim

2025-10-14T00:17:07.145 INFO (pid:66408) [plugin] - coc.nvim initialized with node: v18.19.1 after 283
2025-10-14T00:17:07.159 INFO (pid:66408) [services] - LanguageClient lua state change: stopped => starting
2025-10-14T00:17:07.163 INFO (pid:66408) [language-client-index] - Language server "lua" started with 66504
2025-10-14T00:17:07.303 INFO (pid:66408) [services] - LanguageClient lua state change: starting => running
2025-10-14T00:17:07.313 INFO (pid:66408) [services] - service lua started
2025-10-14T08:31:04.257 INFO (pid:66408) [attach] - Request action: stopCompletion [ '' ]
2025-10-14T08:31:08.660 INFO (pid:66408) [attach] - receive notification: showInfo []

And btw. it doesn't matter which language server is used. E.g. I also observe these laggs, when editing lua files.

[xR3b0rn]

Ah, I had an flash of inspiration: When not running nvim inside tmux, everything suddenly runs smoothly.

But I don't have any idea, why tmux is ruining the preformance there...

[xR3b0rn]

Another update:
Yesterday I did everything in one tmux session:

• Installed coc.nvim
• Tested coc.nvim

After realizing today that the lag was caused by tmux, I killed my tmux session and restarted it - now everything seems to run smoothly.

Great plugin!

[fannheyward]

Yes, tmux multiplexer will slow down in some cases, search tmux multiplexer slow for more info.