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Commit 2cd3220

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Merge branch '189-show-locks' into 'master'
feat: show locks for a single query analyzed with EXPLAIN (#189) Closes #189 See merge request postgres-ai/joe!175
2 parents 66c4031 + 7c42b86 commit 2cd3220

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3 files changed

+112
-6
lines changed

3 files changed

+112
-6
lines changed

‎pkg/bot/command/explain.go

Lines changed: 58 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -10,6 +10,8 @@ import (
1010
"strings"
1111

1212
"github.com/jackc/pgtype/pgxtype"
13+
"github.com/jackc/pgx/v4"
14+
"github.com/jackc/pgx/v4/pgxpool"
1315
"github.com/pkg/errors"
1416

1517
"gitlab.com/postgres-ai/database-lab/v2/pkg/log"
@@ -30,6 +32,9 @@ const (
3032
// Query Explain prefixes.
3133
queryExplain = "EXPLAIN (FORMAT TEXT) "
3234
queryExplainAnalyze = "EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS, FORMAT JSON) "
35+
36+
// locksTitle shows locks for a single query analyzed with EXPLAIN.
37+
locksTitle = "*Query heavy locks:*\n"
3338
)
3439

3540
// Explain runs an explain query.
@@ -41,29 +46,51 @@ func Explain(ctx context.Context, msgSvc connection.Messenger, command *platform
4146

4247
serviceConn, err := getConn(ctx, session.Pool)
4348
if err != nil {
44-
log.Err("failed to get connection:", err)
49+
log.Err("failed to get connection:", err)
4550
return err
4651
}
4752

4853
defer func() {
54+
if err := serviceConn.Conn().Close(ctx); err != nil {
55+
log.Err("failed to close connection: ", err)
56+
}
57+
4958
serviceConn.Release()
5059
}()
5160

61+
tx, err := serviceConn.BeginTx(ctx, pgx.TxOptions{})
62+
if err != nil {
63+
log.Err("failed to begin transaction:", err)
64+
return err
65+
}
66+
67+
defer func() {
68+
if err := tx.Rollback(ctx); err != nil {
69+
log.Err("failed to rollback transaction:", err)
70+
}
71+
}()
72+
73+
txPID, err := querier.GetBackendPID(ctx, tx)
74+
if err != nil {
75+
log.Err("failed to get backend PID:", err)
76+
return err
77+
}
78+
5279
cmd := NewPlan(command, msg, session.CloneConnection, msgSvc)
5380
msgInitText, err := cmd.explainWithoutExecution(ctx)
5481
if err != nil {
5582
return errors.Wrap(err, "failed to run explain without execution")
5683
}
5784

58-
// Explain analyze request and processing.
59-
explainAnalyze, err := querier.DBQueryWithResponse(ctx, session.CloneConnection, queryExplainAnalyze+command.Query)
85+
explainAnalyze, err := querier.DBQueryWithResponse(ctx, tx, queryExplainAnalyze+command.Query)
6086
if err != nil {
6187
return err
6288
}
6389

64-
if err := serviceConn.Conn().Close(ctx); err != nil {
65-
log.Err("Failed to close connection: ", err)
66-
return err
90+
// Observe query locks.
91+
result, err := observeLocks(ctx, session.Pool, txPID)
92+
if err != nil {
93+
log.Err("failed to observe locks:", err)
6794
}
6895

6996
command.PlanExecJSON = explainAnalyze
@@ -84,6 +111,14 @@ func Explain(ctx context.Context, msgSvc connection.Messenger, command *platform
84111
msg.SetText(msgInitText)
85112
msg.AppendText(fmt.Sprintf("*Plan with execution:*\n```%s```", planExecPreview))
86113

114+
// Show query locks.
115+
tableString := &strings.Builder{}
116+
querier.RenderTable(tableString, result)
117+
118+
queryLocks := tableString.String()
119+
command.QueryLocks = strings.Trim(queryLocks, "`")
120+
msg.AppendText(locksTitle + queryLocks)
121+
87122
if err = msgSvc.UpdateText(msg); err != nil {
88123
log.Err("Show the plan with execution:", err)
89124

@@ -153,6 +188,23 @@ func Explain(ctx context.Context, msgSvc connection.Messenger, command *platform
153188
return nil
154189
}
155190

191+
func observeLocks(ctx context.Context, db *pgxpool.Pool, txPID int) ([][]string, error) {
192+
observeConn, err := getConn(ctx, db)
193+
if err != nil {
194+
return nil, err
195+
}
196+
197+
defer func() {
198+
if err := observeConn.Conn().Close(ctx); err != nil {
199+
log.Err("failed to close observer connection:", err)
200+
}
201+
202+
observeConn.Release()
203+
}()
204+
205+
return querier.ObserveLocks(ctx, observeConn, txPID)
206+
}
207+
156208
func listHypoIndexes(ctx context.Context, db pgxtype.Querier) ([]string, error) {
157209
rows, err := db.Query(ctx, "SELECT indexname FROM hypopg_list_indexes()")
158210
if err != nil {

‎pkg/bot/querier/sql.go

Lines changed: 53 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -34,6 +34,48 @@ func DBQueryWithResponse(ctx context.Context, db pgxtype.Querier, query string)
3434
return runQuery(ctx, db, query)
3535
}
3636

37+
const observeQuery = `with data as (
38+
select
39+
c.relkind,
40+
c.relnamespace::regnamespace,
41+
c.relname,
42+
format(
43+
'%s%s',
44+
nullif(c.relnamespace::regnamespace::text, 'public') || '.',
45+
coalesce(ind.tablename, relname)
46+
) as belongs_to_relation, -- todo: do the same for TOAST tables/indexes?
47+
l.locktype,
48+
l.mode,
49+
l.granted::text,
50+
l.fastpath::text
51+
from pg_locks as l
52+
join pg_class as c on c.oid = l.relation
53+
left join pg_indexes as ind on
54+
c.relkind = 'i'
55+
and indexname = c.relname
56+
and schemaname = c.relnamespace::regnamespace::name
57+
where l.pid = 1ドル
58+
)
59+
select *
60+
from data
61+
where
62+
belongs_to_relation not in ( -- not a perfect solution: <query> can also work with them
63+
'pg_catalog.pg_class',
64+
'pg_catalog.pg_indexes',
65+
'pg_catalog.pg_index',
66+
'pg_catalog.pg_locks',
67+
'pg_catalog.pg_namespace',
68+
'pg_catalog.pg_tablespace'
69+
)
70+
order by
71+
belongs_to_relation,
72+
case relkind when 'r' then 0 when 'v' then 1 when 'i' then 9 else 5 end;`
73+
74+
// ObserveLocks selects locks details filtered by pid.
75+
func ObserveLocks(ctx context.Context, db pgxtype.Querier, pid int) ([][]string, error) {
76+
return runTableQuery(ctx, db, observeQuery, pid)
77+
}
78+
3779
func runQuery(ctx context.Context, db pgxtype.Querier, query string) (string, error) {
3880
log.Dbg("DB query:", query)
3981

@@ -148,3 +190,14 @@ func clarifyQueryError(query []byte, err error) error {
148190

149191
return err
150192
}
193+
194+
// GetBackendPID returns backend pid.
195+
func GetBackendPID(ctx context.Context, conn pgxtype.Querier) (int, error) {
196+
var backendPID int
197+
198+
if err := conn.QueryRow(ctx, `select pg_backend_pid()`).Scan(&backendPID); err != nil {
199+
return backendPID, err
200+
}
201+
202+
return backendPID, nil
203+
}

‎pkg/services/platform/platform.go

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -43,6 +43,7 @@ type Command struct {
4343
PlanExecJSON string `json:"plan_execution_json"`
4444
Recommendations string `json:"recommendations"`
4545
Stats string `json:"stats"`
46+
QueryLocks string `json:"query_locks"`
4647

4748
Error string `json:"error"`
4849

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