[#309] locode: Parallelize DB generation

For v0.4.0 release:
Before:
```
Executed in  571.64 secs    fish           external
   usr time  283.07 secs  744.00 micros  283.07 secs
   sys time    8.41 secs  179.00 micros    8.41 secs
```

After:
```
Executed in   54.23 secs    fish           external
   usr time  418.65 secs    1.01 millis  418.65 secs
   sys time    0.61 secs    0.25 millis    0.60 secs
```
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

CHANGELOG.md

@@ -9,6 +9,7 @@ Changelog for FrostFS Node
 - Reload pprof and metrics on SIGHUP for ir (#125)
 
 ### Changed
+- `frostfs-cli util locode generate` is now much faster (#309)
 ### Fixed
 - Take network settings into account during netmap contract update (#100)
 - Read config files from dir even if config file not provided via `--config` for node (#238)

pkg/util/locode/db/boltdb/calls.go

@@ -103,7 +103,7 @@ func recordFromValue(data []byte) (*locodedb.Record, error) {
 // Must not be called before successful Open call.
 // Must not be called in read-only mode: behavior is undefined.
 func (db *DB) Put(key locodedb.Key, rec locodedb.Record) error {
-	return db.bolt.Update(func(tx *bbolt.Tx) error {
+	return db.bolt.Batch(func(tx *bbolt.Tx) error {
 		countryKey, err := countryBucketKey(key.CountryCode())
 		if err != nil {
 			return err

pkg/util/locode/db/db.go

@@ -3,8 +3,10 @@ package locodedb
 import (
 	"errors"
 	"fmt"
+	"runtime"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/locode"
+	"golang.org/x/sync/errgroup"
 )
 
 // SourceTable is an interface of the UN/LOCODE table.
@@ -75,7 +77,20 @@ type NamesDB interface {
 
 // FillDatabase generates the FrostFS location database based on the UN/LOCODE table.
 func FillDatabase(table SourceTable, airports AirportDB, continents ContinentsDB, names NamesDB, db DB) error {
-	return table.IterateAll(func(tableRecord locode.Record) error {
+	var errG errgroup.Group
+
+	// Pick some sane default, after this the performance stopped increasing.
+	errG.SetLimit(runtime.NumCPU() * 4)
+	_ = table.IterateAll(func(tableRecord locode.Record) error {
+		errG.Go(func() error {
+			return processTableRecord(tableRecord, airports, continents, names, db)
+		})
+		return nil
+	})
+	return errG.Wait()
+}
+
+func processTableRecord(tableRecord locode.Record, airports AirportDB, continents ContinentsDB, names NamesDB, db DB) error {
 	if tableRecord.LOCODE.LocationCode() == "" {
 		return nil
 	}
@@ -149,7 +164,6 @@ func FillDatabase(table SourceTable, airports AirportDB, continents ContinentsDB
 	dbRecord.SetContinent(continent)
 
 	return db.Put(*dbKey, *dbRecord)
-	})
 }
 
 // LocodeRecord returns the record from the FrostFS location database