feat: allow setting limit in pg_stat_statements

Add `.limit` CLI flag to `stat_statements` collector to allow setting a custom number of queries to be returned. Signed-off-by: Cristian Greco <cristian@regolo.cc>

Author: cristiangreco

collector/pg_stat_statements.go

@@ -24,11 +24,15 @@ import (
 "github.com/prometheus/client_golang/prometheus"
 )
 
-const statStatementsSubsystem = "stat_statements"
+const (
+statStatementsSubsystem = "stat_statements"
+defaultStatementLimit = "100"
+)
 
 var (
 includeQueryFlag *bool = nil
 statementLengthFlag *uint = nil
+statementLimitFlag *uint = nil
 )
 
 func init() {
@@ -47,19 +51,26 @@ func init() {
 "Maximum length of the statement text.").
 Default("120").
 Uint()
+statementLimitFlag = kingpin.Flag(
+fmt.Sprint(collectorFlagPrefix, statStatementsSubsystem, ".limit"),
+"Maximum number of statements to return.").
+Default(defaultStatementLimit).
+Uint()
 }
 
 type PGStatStatementsCollector struct {
 log *slog.Logger
 includeQueryStatement bool
 statementLength uint
+statementLimit uint
 }
 
 func NewPGStatStatementsCollector(config collectorConfig) (Collector, error) {
 return &PGStatStatementsCollector{
 log: config.logger,
 includeQueryStatement: *includeQueryFlag,
 statementLength: *statementLengthFlag,
+statementLimit: *statementLimitFlag,
 }, nil
 }
 
@@ -126,9 +137,9 @@ const (
 FROM pg_stat_statements
 )
 ORDER BY seconds_total DESC
-LIMIT 100;`
+LIMIT %s;`
 
-pgStatStatementsNewQuery = `SELECT
+pgStatStatementsQuery_PG13 = `SELECT
 pg_get_userbyid(userid) as user,
 pg_database.datname,
 pg_stat_statements.queryid,
@@ -148,7 +159,7 @@ const (
 FROM pg_stat_statements
 )
 ORDER BY seconds_total DESC
-LIMIT 100;`
+LIMIT %s;`
 
 pgStatStatementsQuery_PG17 = `SELECT
 pg_get_userbyid(userid) as user,
@@ -170,7 +181,7 @@ const (
 FROM pg_stat_statements
 )
 ORDER BY seconds_total DESC
-LIMIT 100;`
+LIMIT %s;`
 )
 
 func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
@@ -179,20 +190,24 @@ func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instanc
 case instance.version.GE(semver.MustParse("17.0.0")):
 queryTemplate = pgStatStatementsQuery_PG17
 case instance.version.GE(semver.MustParse("13.0.0")):
-queryTemplate = pgStatStatementsNewQuery
+queryTemplate = pgStatStatementsQuery_PG13
 default:
 queryTemplate = pgStatStatementsQuery
 }
-var querySelect = ""
+querySelect := ""
 if c.includeQueryStatement {
 querySelect = fmt.Sprintf(pgStatStatementQuerySelect, c.statementLength)
 }
-query := fmt.Sprintf(queryTemplate, querySelect)
+statementLimit := defaultStatementLimit
+if c.statementLimit > 0 {
+statementLimit = fmt.Sprintf("%d", c.statementLimit)
+}
+query := fmt.Sprintf(queryTemplate, querySelect, statementLimit)
 
 db := instance.getDB()
 rows, err := db.QueryContext(ctx, query)
 
-var presentQueryIds = make(map[string]struct{})
+presentQueryIds := make(map[string]struct{})
 
 if err != nil {
 return err