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[+] implement parallel source discovery #1378

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Merged
pashagolub merged 4 commits into from
Apr 29, 2026
Merged

[+] implement parallel source discovery #1378

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89cb5eb
[+] implement parallel source discovery
pashagolub Apr 24, 2026
99cc08f
`reaper.WriteInstanceDown()` accepts name as an argument
pashagolub Apr 24, 2026
a47b7fb
use `on_error` callback in `Sources.ResolveDatabases()`
pashagolub Apr 24, 2026
791941d
use const instead of hard-coded value
pashagolub Apr 29, 2026
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2 changes: 1 addition & 1 deletion internal/cmdopts/cmdsource.go
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,7 @@ func (cmd *SourceResolveCommand) Execute(args []string) error {
}
}
}
conns, err := foundSources.ResolveDatabases()
conns, err := foundSources.ResolveDatabases(nil)
if err != nil {
return err
}
Expand Down
2 changes: 1 addition & 1 deletion internal/reaper/database.go
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Original file line number Diff line number Diff line change
Expand Up @@ -438,7 +438,7 @@ func (r *Reaper) GetInstanceUpMeasurement(ctx context.Context, md *sources.Sourc
return metrics.Measurements{
metrics.Measurement{
metrics.EpochColumnName: time.Now().UnixNano(),
"instance_up": func() int {
specialMetricInstanceUp: func() int {
if md.Conn.Ping(ctx) == nil {
return 1
}
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11 changes: 7 additions & 4 deletions internal/reaper/reaper.go
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Expand Up @@ -101,7 +101,7 @@ func (r *Reaper) Reap(ctx context.Context) {
ctx = log.WithLogger(ctx, srcL)

if monitoredSource.Connect(ctx, r.Sources) != nil {
r.WriteInstanceDown(monitoredSource)
r.WriteInstanceDown(monitoredSource.Name)
srcL.Warning("could not init connection, retrying on next iteration")
continue
}
Expand Down Expand Up @@ -405,9 +405,12 @@ func (r *Reaper) LoadSources(ctx context.Context) (err error) {
return err
}
srcs = slices.DeleteFunc(srcs, func(s sources.Source) bool {
// filter out disabled sources and sources with group not in the list of groups to monitor
return !s.IsEnabled || len(r.Sources.Groups) > 0 && !slices.Contains(r.Sources.Groups, s.Group)
})
if newSrcs, err = srcs.ResolveDatabases(); err != nil {

if newSrcs, err = srcs.ResolveDatabases(r.WriteInstanceDown); err != nil {
// discover dtabases for continuous monitoring sources
r.logger.WithError(err).Error("could not resolve databases from sources")
}

Expand All @@ -432,9 +435,9 @@ func (r *Reaper) LoadSources(ctx context.Context) (err error) {
}

// WriteInstanceDown writes instance_up = 0 metric to sinks for the given source
func (r *Reaper) WriteInstanceDown(md *sources.SourceConn) {
func (r *Reaper) WriteInstanceDown(name string) {
r.measurementCh <- metrics.MeasurementEnvelope{
DBName: md.Name,
DBName: name,
MetricName: specialMetricInstanceUp,
Data: metrics.Measurements{metrics.Measurement{
metrics.EpochColumnName: time.Now().UnixNano(),
Expand Down
2 changes: 1 addition & 1 deletion internal/reaper/reaper_test.go
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Expand Up @@ -593,5 +593,5 @@ func TestWriteMeasurements(t *testing.T) {
SinksWriter: err,
})
go r.WriteMeasurements(ctx)
r.WriteInstanceDown(&sources.SourceConn{})
r.WriteInstanceDown("foo")
}
33 changes: 25 additions & 8 deletions internal/sources/resolver.go
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Expand Up @@ -14,6 +14,7 @@ import (
"net/url"
"os"
"strings"
"sync"
"time"

jsoniter "github.com/json-iterator/go"
Expand All @@ -25,16 +26,32 @@ import (
"go.uber.org/zap"
)

// ResolveDatabases() updates list of monitored objects from continuous monitoring sources, e.g. patroni
func (srcs Sources) ResolveDatabases() (_ SourceConns, err error) {
// ResolveDatabases() updates list of monitored objects from continuous monitoring sources, e.g. patroni.
// Each source is resolved concurrently so that a slow or unreachable source does not block the others.
func (srcs Sources) ResolveDatabases(onError func(string)) (_ SourceConns, err error) {
type result struct {
dbs SourceConns
err error
}
results := make([]result, len(srcs))
var wg sync.WaitGroup
for i, s := range srcs {
wg.Go(func() {
dbs, e := s.ResolveDatabases()
results[i] = result{dbs, e}
})
}
wg.Wait()
resolvedDbs := make(SourceConns, 0, len(srcs))
for _, s := range srcs {
if !s.IsEnabled {
continue
for i, res := range results {
if res.err != nil {
if onError != nil {
onError(srcs[i].Name)
}
Comment on lines +48 to +50
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@0xgouda 0xgouda Apr 28, 2026 •
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I have a concern here that can be reproduced with the following steps:

  1. Define a target that happens to be unreachable and is of the kind postgres-continuous-discovery
  2. pgwatch writes instance_up=0 for the target for a while with dbname = sourceName
  3. The target becomes alive
  4. pgwatch runs for a while and now writes the updated instance_up = 1, but with a new dbname = sourceName + _ + realDbname
  5. The target is down again and its instance_up = 0 is written with dbname = sourceName + _ + realDbname

So the full instance uptime history becomes a bit disconnected, with different dbname[s].

But generally, I think that's the best we can do, just wanted to note this behaviour.

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@pashagolub pashagolub Apr 28, 2026

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Good catch! We could use source instead of dbname. This way we will know for sure at which point that happened

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@0xgouda 0xgouda Apr 28, 2026

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Can you explain more?

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@pashagolub pashagolub Apr 28, 2026 •
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// WriteInstanceDown writes instance_up = 0 metric to sinks for the given source
func (r *Reaper) WriteInstanceDown(md *sources.SourceConn) {
	r.measurementCh <- metrics.MeasurementEnvelope{
		DBName:     md.Name,
		MetricName: specialMetricInstanceUp,
		Data: metrics.Measurements{metrics.Measurement{
			metrics.EpochColumnName: time.Now().UnixNano(),
			"kind": string(md.Kind),
		//  ^^^^^^^^^^^^^^^^^^^^^^^
			specialMetricInstanceUp: 0},
		},
	}
}

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@pashagolub pashagolub Apr 28, 2026

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this way grafana could distinguish regular databases vs all other

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@0xgouda 0xgouda Apr 29, 2026

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I don't think adding the kind to the measurements will help.

What if we have 2+ postgres-continuous-discovery/patroni sources? Grouping by kind then will be useless.

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@0xgouda 0xgouda Apr 29, 2026 •
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And again, I guess what we have already is the best we can do, since we won't be able to add any instance identifiers (i.e., sys_id) to the measurements before connecting at least once.

But then, in Grafana, one might have 2 panels like:
instance uptime history grouped by sys_id
and
instance uptime history for instances with unknown sys_id

and they should complement each other, to give the full uptime history view.

logger.WithField("source", srcs[i].Name).WithError(res.err).Error("could not resolve databases from source")
err = errors.Join(err, res.err)
}
dbs, e := s.ResolveDatabases()
err = errors.Join(err, e)
resolvedDbs = append(resolvedDbs, dbs...)
resolvedDbs = append(resolvedDbs, res.dbs...)
}
return resolvedDbs, err
}
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