Fast Index¶

To speed up the search, create a fast index for each gallery, using the findface-tarantool-build-index utility delivered with the console installer. The utility is independent of the findface-tarantool-server component and can be installed either on the localhost or on a remote host with access to Tarantool.

To create a fast index, do the following:

If you have installed the FindFace core step-by-step, install the findface-tarantool-build-index utility.
```
sudo apt install findface-tarantool-build-index
```
Create a fast index for your gallery (testgal in the case-study). First, connect to the Tarantool console.

Important

The gallery must not be empty. See Direct API Requests to Tarantool to fill the gallery with faces.

Note

You have to repeat the fast index creation on each findface-tarantool-server shard.
```
tarantoolctl connect 127.0.0.1:33001
```
Run prepare_preindex. Each element of the gallery will be moved from the linear space to preindex:
```
127.0.0.1:33001> FindFace.Gallery.new("testgal"):prepare_preindex()
---
...
```

Prepare a file for generating the index:

127.0.0.1:33001> FindFace.Gallery.new("testgal"):save_preindex("/tmp/preindex.bin")
---
...

Launch index generation with the findface-tarantool-build-index utility (see --help for additional options). Depending on the number of elements, this process can take up to several hours and can be done on a separate, more powerful machine (for huge galleries we recommend c4.8xlarge amazon, for example, spot-instance).

findface-build-index --input /tmp/preindex.bin --output /opt/ntech/var/lib/tarantool/default/index/testgal.idx --facen_size 320
Config values:
.input = /tmp/preindex.bin
.output = /opt/ntech/var/lib/tarantool/default/index/testgal.idx
.facen_size = 320
.param_m = 12
.param_ef = 500
.limit = 4294967295

Building index: [XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX] 100% ; 3 / 3
Index saved at /opt/ntech/var/lib/tarantool/default/index/testgal.idx

Delete the preindex.bin file.
```
sudo rm /tmp/preindex.bin
```
Enable the fast index for the gallery.

Note

If Tarantool works as a replica set, copy the index file (.idx) from the master instance to the same path on the replica before enabling the fast index for the master instance (:use_index).

Tip

Do not forget to remove obsolete index files on the replica in order to avoid unnecessary index transitions, should the master instance and replica be heavily out of sync.
```
127.0.0.1:33001> FindFace.Gallery.new("testgal"):preindex_to_index()
---
...
127.0.0.1:33001> sudo FindFace.Gallery.new("testgal"):use_index("/opt/ntech/var/lib/tarantool/default/index/testgal.idx")
---
...
```
Search through the gallery should now be significantly faster. Information about the index remains in the service space, so when you restart Tarantool, the index will also be uploaded.

Warning

Do not move the index file to another location!