feat: add database block count to prometheus to improve alert monitor…

…ing (#74)

## Description

Fixes [BDU-542](https://forbole.atlassian.net/browse/BDU-542)

## Checklist
- [x] Targeted PR against correct branch.
- [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
- [ ] Wrote unit tests.  
- [x] Re-reviewed `Files changed` in the Github PR explorer.

CHANGELOG.md

@@ -1,3 +1,7 @@
+## Unreleased
+### Changes
+- ([\#74](https://github.com/forbole/juno/pull/74)) Added database block count to prometheus to improve alert monitoring
+
 ## v3.4.0
 ### Changes
 - ([\#71](https://github.com/forbole/juno/pull/71)) Retry RPC client connection upon failure instead of panic

database/database.go

@@ -26,6 +26,9 @@ type Database interface {
 	// NOTE. For each transaction inside txs, SaveTx will be called as well.
 	SaveBlock(block *types.Block) error
 
+	// GetTotalBlocks returns total number of blocks stored in database.
+	GetTotalBlocks() int64
+
 	// SaveTx will be called to save each transaction contained inside a block.
 	// An error is returned if the operation fails.
 	SaveTx(tx *types.Tx) error

database/postgresql/postgresql.go

@@ -125,6 +125,17 @@ VALUES ($1, $2, $3, $4, $5, $6) ON CONFLICT DO NOTHING`
 	return err
 }
 
+// GetTotalBlocks implements database.Database
+func (db *Database) GetTotalBlocks() int64 {
+	var blockCount int64
+	err := db.Sql.QueryRow(`SELECT count(*) FROM block;`).Scan(&blockCount)
+	if err != nil {
+		return 0
+	}
+
+	return blockCount
+}
+
 // SaveTx implements database.Database
 func (db *Database) SaveTx(tx *types.Tx) error {
 	var partitionID int64

logging/prometheus.go

@@ -37,6 +37,14 @@ var ErrorCount = prometheus.NewCounter(
 	},
 )
 
+var DbBlockCount = prometheus.NewGaugeVec(
+	prometheus.GaugeOpts{
+		Name: "juno_db_total_blocks",
+		Help: "Total number of blocks in database.",
+	},
+	[]string{"total_blocks_in_db"},
+)
+
 func init() {
 	err := prometheus.Register(StartHeight)
 	if err != nil {
@@ -57,4 +65,9 @@ func init() {
 	if err != nil {
 		panic(err)
 	}
+
+	err = prometheus.Register(DbBlockCount)
+	if err != nil {
+		panic(err)
+	}
 }

parser/worker.go

@@ -332,5 +332,8 @@ func (w Worker) ExportTxs(txs []*types.Tx) error {
 		}
 	}
 
+	totalBlocks := w.db.GetTotalBlocks()
+	logging.DbBlockCount.WithLabelValues("total_blocks_in_db").Set(float64(totalBlocks))
+
 	return nil
 }