Slow wallet loading

[deeplytical]

When start litecoinzd it tooks several hours to load the wallet and to get respond from litecoinz-cli getinfo for example.
When executing ./litecoinz-cli getinfo I get this

error code: -28
error message:
Rescanning...

The wallet is not responsive for several hours, on debug log I have these lines:

2020-11-02T08:35:23Z Setting Inital Sapling Witness for tx 75b999f7b56f5d6c0726bac00388aca449d6a710821423a8efb55d7b0b179efd, 155242 of 156713
2020-11-02T08:35:23Z Setting Inital Sapling Witness for tx e4bae7ef8466f2335936dddd1e21cc3590a42d8fd0ce6d65f228ea77cd45d9fe, 156027 of 156713
2020-11-02T08:35:54Z Building Witnesses for block 405000 0.6889 complete
2020-11-02T08:35:57Z Building Witnesses for block 405100 0.6890 complete
2020-11-02T08:36:01Z Building Witnesses for block 405200 0.6892 complete
2020-11-02T08:36:05Z Building Witnesses for block 405300 0.6894 complete
.......................................................
.......................................................
.......................................................
2020-11-02T10:30:37Z Building Witnesses for block 587300 0.9989 complete
2020-11-02T10:30:40Z Building Witnesses for block 587400 0.9991 complete
2020-11-02T10:30:44Z Building Witnesses for block 587500 0.9993 complete
2020-11-02T10:30:47Z Building Witnesses for block 587600 0.9995 complete
2020-11-02T10:30:51Z Building Witnesses for block 587700 0.9996 complete
2020-11-02T10:30:54Z Building Witnesses for block 587800 0.9998 complete
2020-11-02T10:30:58Z Building Witnesses for block 587900 1.0000 complete

Expected behavior

I expect when start litecoinzd the wallet to be available for commands executing and to be responsive after no more than 1 min

Actual behavior

As u can see from the log - this rescaning take too long time and this happens always when use this wallet.

To reproduce

This happens every time when use this wallet - it is the wallet used by the mining pool, the size of the wallet is too big - 326 MB . The wallet was used with the old litecoinzd version ( 2.0.5) and the issue is happening after wallet has been upgraded for the new litecoinzd version ( 3.0.1). Command used for upgrading - ./litecoinzd -upgradewallet -rescan -reindex. After this every time when execute ./litecoinzd the problem described above occurs.

System information

The problem occurs for Ubuntu 18.04 ( 4 GB RAM 3.0 ghz CPU 2 core ) and Fedora 30 ( 8 GB RAM, 2.4 GHZ 8 core )

[MarkLTZ]

Dear @deeplytical
thank you very much for your feedback. The issue is caused by a lot of unspent notes in your wallet. I'm checking now for a better witness computation.

Regards,
Mark