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charlieviethcharlievieth
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sqlite3: reduce C to Go string conversions in SQLiteConn.{query,exec}
This commit fixes an issue where SQLiteConn.{exec,query} would use an exponential amount of memory when processing a prepared statement that consisted of multiple SQL statements ("stmt 1; stmt 2; ..."). Previously both exec/query used SQLiteConn.prepare() which converts the "tail" pointer set by sqlite3_prepare_v2() back into a Go string, which then has to be converted back to a C string for the next call to prepare() (assuming there are multiple SQL statements in the provided query). This commit fixes this by changing both exec and query to use the returned "tail" pointer for the next call to exec/query. It also changes prepare() to use pointer arithmetic to calculate the offset of the remaining "tail" portion of the query as a substring of the original query. This saves a call to C.GoString() and an allocation. Benchmarks: ``` goos: darwin goarch: arm64 pkg: github.com/mattn/go-sqlite3 │ base.10.txt │ new.10.txt │ │ sec/op │ sec/op vs base │ Suite/BenchmarkExec-10 1.351µ ± 1% 1.247µ ± 1% -7.74% (p=0.000 n=10) Suite/BenchmarkQuery-10 3.830µ ± 1% 3.558µ ± 1% -7.11% (p=0.000 n=10) Suite/BenchmarkParams-10 4.221µ ± 0% 4.228µ ± 1% ~ (p=1.000 n=10) Suite/BenchmarkStmt-10 2.906µ ± 1% 2.864µ ± 1% -1.45% (p=0.001 n=10) Suite/BenchmarkRows-10 149.1µ ± 4% 148.2µ ± 1% -0.61% (p=0.023 n=10) Suite/BenchmarkStmtRows-10 147.3µ ± 1% 145.6µ ± 0% -1.16% (p=0.000 n=10) Suite/BenchmarkExecStep-10 1898.9µ ± 3% 889.0µ ± 1% -53.18% (p=0.000 n=10) Suite/BenchmarkQueryStep-10 1848.0µ ± 1% 894.6µ ± 1% -51.59% (p=0.000 n=10) geomean 38.56µ 31.30µ -18.84% │ base.10.txt │ new.10.txt │ │ B/op │ B/op vs base │ Suite/BenchmarkExec-10 184.0 ± 0% 176.0 ± 0% -4.35% (p=0.000 n=10) Suite/BenchmarkQuery-10 864.0 ± 0% 856.0 ± 0% -0.93% (p=0.000 n=10) Suite/BenchmarkParams-10 1.289Ki ± 0% 1.281Ki ± 0% -0.61% (p=0.000 n=10) Suite/BenchmarkStmt-10 1.078Ki ± 0% 1.078Ki ± 0% ~ (p=1.000 n=10) ¹ Suite/BenchmarkRows-10 34.45Ki ± 0% 34.45Ki ± 0% -0.02% (p=0.000 n=10) Suite/BenchmarkStmtRows-10 34.40Ki ± 0% 34.40Ki ± 0% ~ (p=1.000 n=10) ¹ Suite/BenchmarkExecStep-10 5334.61Ki ± 0% 70.41Ki ± 0% -98.68% (p=0.000 n=10) Suite/BenchmarkQueryStep-10 5397.4Ki ± 0% 133.2Ki ± 0% -97.53% (p=0.000 n=10) geomean 17.06Ki 6.208Ki -63.62% ¹ all samples are equal │ base.10.txt │ new.10.txt │ │ allocs/op │ allocs/op vs base │ Suite/BenchmarkExec-10 13.00 ± 0% 12.00 ± 0% -7.69% (p=0.000 n=10) Suite/BenchmarkQuery-10 46.00 ± 0% 45.00 ± 0% -2.17% (p=0.000 n=10) Suite/BenchmarkParams-10 54.00 ± 0% 53.00 ± 0% -1.85% (p=0.000 n=10) Suite/BenchmarkStmt-10 49.00 ± 0% 49.00 ± 0% ~ (p=1.000 n=10) ¹ Suite/BenchmarkRows-10 2.042k ± 0% 2.041k ± 0% -0.05% (p=0.000 n=10) Suite/BenchmarkStmtRows-10 2.038k ± 0% 2.038k ± 0% ~ (p=1.000 n=10) ¹ Suite/BenchmarkExecStep-10 13.000k ± 0% 8.004k ± 0% -38.43% (p=0.000 n=10) Suite/BenchmarkQueryStep-10 11.013k ± 0% 6.017k ± 0% -45.36% (p=0.000 n=10) geomean 418.6 359.8 -14.04% ¹ all samples are equal ```
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‎sqlite3.go‎

Lines changed: 72 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,7 @@ package sqlite3
3030
#endif
3131
#include <stdlib.h>
3232
#include <string.h>
33+
#include <ctype.h>
3334
3435
#ifdef __CYGWIN__
3536
# include <errno.h>
@@ -90,6 +91,16 @@ _sqlite3_exec(sqlite3* db, const char* pcmd, long long* rowid, long long* change
9091
return rv;
9192
}
9293
94+
static const char *
95+
_trim_leading_spaces(const char *str) {
96+
if (str) {
97+
while (isspace(*str)) {
98+
str++;
99+
}
100+
}
101+
return str;
102+
}
103+
93104
#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY
94105
extern int _sqlite3_step_blocking(sqlite3_stmt *stmt);
95106
extern int _sqlite3_step_row_blocking(sqlite3_stmt* stmt, long long* rowid, long long* changes);
@@ -110,7 +121,11 @@ _sqlite3_step_row_internal(sqlite3_stmt* stmt, long long* rowid, long long* chan
110121
static int
111122
_sqlite3_prepare_v2_internal(sqlite3 *db, const char *zSql, int nBytes, sqlite3_stmt **ppStmt, const char **pzTail)
112123
{
113-
return _sqlite3_prepare_v2_blocking(db, zSql, nBytes, ppStmt, pzTail);
124+
int rv = _sqlite3_prepare_v2_blocking(db, zSql, nBytes, ppStmt, pzTail);
125+
if (pzTail) {
126+
*pzTail = _trim_leading_spaces(*pzTail);
127+
}
128+
return rv;
114129
}
115130
116131
#else
@@ -133,7 +148,11 @@ _sqlite3_step_row_internal(sqlite3_stmt* stmt, long long* rowid, long long* chan
133148
static int
134149
_sqlite3_prepare_v2_internal(sqlite3 *db, const char *zSql, int nBytes, sqlite3_stmt **ppStmt, const char **pzTail)
135150
{
136-
return sqlite3_prepare_v2(db, zSql, nBytes, ppStmt, pzTail);
151+
int rv = sqlite3_prepare_v2(db, zSql, nBytes, ppStmt, pzTail);
152+
if (pzTail) {
153+
*pzTail = _trim_leading_spaces(*pzTail);
154+
}
155+
return rv;
137156
}
138157
#endif
139158
@@ -858,25 +877,33 @@ func (c *SQLiteConn) Exec(query string, args []driver.Value) (driver.Result, err
858877
}
859878

860879
func (c *SQLiteConn) exec(ctx context.Context, query string, args []driver.NamedValue) (driver.Result, error) {
880+
pquery := C.CString(query)
881+
op := pquery // original pointer
882+
defer C.free(unsafe.Pointer(op))
883+
884+
var stmtArgs []driver.NamedValue
885+
var tail *C.char
886+
s := new(SQLiteStmt) // escapes to the heap so reuse it
861887
start := 0
862888
for {
863-
s, err := c.prepare(ctx, query)
864-
if err != nil {
865-
return nil, err
889+
*s = SQLiteStmt{c: c} // reset
890+
rv := C._sqlite3_prepare_v2_internal(c.db, pquery, C.int(-1), &s.s, &tail)
891+
if rv != C.SQLITE_OK {
892+
return nil, c.lastError()
866893
}
894+
867895
var res driver.Result
868-
if s.(*SQLiteStmt).s != nil {
869-
stmtArgs := make([]driver.NamedValue, 0, len(args))
896+
if s.s != nil {
870897
na := s.NumInput()
871898
if len(args)-start < na {
872-
s.Close()
899+
s.finalize()
873900
return nil, fmt.Errorf("not enough args to execute query: want %d got %d", na, len(args))
874901
}
875902
// consume the number of arguments used in the current
876903
// statement and append all named arguments not
877904
// contained therein
878905
if len(args[start:start+na]) > 0 {
879-
stmtArgs = append(stmtArgs, args[start:start+na]...)
906+
stmtArgs = append(stmtArgs[:0], args[start:start+na]...)
880907
for i := range args {
881908
if (i < start || i >= na) && args[i].Name != "" {
882909
stmtArgs = append(stmtArgs, args[i])
@@ -886,23 +913,23 @@ func (c *SQLiteConn) exec(ctx context.Context, query string, args []driver.Named
886913
stmtArgs[i].Ordinal = i + 1
887914
}
888915
}
889-
res, err = s.(*SQLiteStmt).exec(ctx, stmtArgs)
916+
var err error
917+
res, err = s.exec(ctx, stmtArgs)
890918
if err != nil && err != driver.ErrSkip {
891-
s.Close()
919+
s.finalize()
892920
return nil, err
893921
}
894922
start += na
895923
}
896-
tail := s.(*SQLiteStmt).t
897-
s.Close()
898-
if tail == "" {
924+
s.finalize()
925+
if tail == nil || *tail == '\000' {
899926
if res == nil {
900927
// https://github.com/mattn/go-sqlite3/issues/963
901928
res = &SQLiteResult{0, 0}
902929
}
903930
return res, nil
904931
}
905-
query = tail
932+
pquery = tail
906933
}
907934
}
908935

@@ -919,22 +946,29 @@ func (c *SQLiteConn) Query(query string, args []driver.Value) (driver.Rows, erro
919946
}
920947

921948
func (c *SQLiteConn) query(ctx context.Context, query string, args []driver.NamedValue) (driver.Rows, error) {
949+
pquery := C.CString(query)
950+
op := pquery // original pointer
951+
defer C.free(unsafe.Pointer(op))
952+
953+
var stmtArgs []driver.NamedValue
954+
var tail *C.char
955+
s := new(SQLiteStmt) // escapes to the heap so reuse it
922956
start := 0
923957
for {
924-
stmtArgs := make([]driver.NamedValue, 0, len(args))
925-
s, err := c.prepare(ctx, query)
926-
if err != nil {
927-
return nil, err
958+
*s = SQLiteStmt{c: c, cls: true} // reset
959+
rv := C._sqlite3_prepare_v2_internal(c.db, pquery, C.int(-1), &s.s, &tail)
960+
if rv != C.SQLITE_OK {
961+
return nil, c.lastError()
928962
}
929-
s.(*SQLiteStmt).cls = true
963+
930964
na := s.NumInput()
931965
if len(args)-start < na {
932966
return nil, fmt.Errorf("not enough args to execute query: want %d got %d", na, len(args)-start)
933967
}
934968
// consume the number of arguments used in the current
935969
// statement and append all named arguments not contained
936970
// therein
937-
stmtArgs = append(stmtArgs, args[start:start+na]...)
971+
stmtArgs = append(stmtArgs[:0], args[start:start+na]...)
938972
for i := range args {
939973
if (i < start || i >= na) && args[i].Name != "" {
940974
stmtArgs = append(stmtArgs, args[i])
@@ -943,19 +977,18 @@ func (c *SQLiteConn) query(ctx context.Context, query string, args []driver.Name
943977
for i := range stmtArgs {
944978
stmtArgs[i].Ordinal = i + 1
945979
}
946-
rows, err := s.(*SQLiteStmt).query(ctx, stmtArgs)
980+
rows, err := s.query(ctx, stmtArgs)
947981
if err != nil && err != driver.ErrSkip {
948-
s.Close()
982+
s.finalize()
949983
return rows, err
950984
}
951985
start += na
952-
tail := s.(*SQLiteStmt).t
953-
if tail == "" {
986+
if tail == nil || *tail == '\000' {
954987
return rows, nil
955988
}
956989
rows.Close()
957-
s.Close()
958-
query = tail
990+
s.finalize()
991+
pquery = tail
959992
}
960993
}
961994

@@ -1818,8 +1851,11 @@ func (c *SQLiteConn) prepare(ctx context.Context, query string) (driver.Stmt, er
18181851
return nil, c.lastError()
18191852
}
18201853
var t string
1821-
if tail != nil && *tail != '\000' {
1822-
t = strings.TrimSpace(C.GoString(tail))
1854+
if tail != nil && *tail != 0 {
1855+
n := int(uintptr(unsafe.Pointer(tail))) - int(uintptr(unsafe.Pointer(pquery)))
1856+
if 0 <= n && n < len(query) {
1857+
t = strings.TrimSpace(query[n:])
1858+
}
18231859
}
18241860
ss := &SQLiteStmt{c: c, s: s, t: t}
18251861
runtime.SetFinalizer(ss, (*SQLiteStmt).Close)
@@ -1913,6 +1949,13 @@ func (s *SQLiteStmt) Close() error {
19131949
return nil
19141950
}
19151951

1952+
func (s *SQLiteStmt) finalize() {
1953+
if s.s != nil {
1954+
C.sqlite3_finalize(s.s)
1955+
s.s = nil
1956+
}
1957+
}
1958+
19161959
// NumInput return a number of parameters.
19171960
func (s *SQLiteStmt) NumInput() int {
19181961
return int(C.sqlite3_bind_parameter_count(s.s))

‎sqlite3_test.go‎

Lines changed: 21 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2111,6 +2111,8 @@ var benchmarks = []testing.InternalBenchmark{
21112111
{Name: "BenchmarkStmt", F: benchmarkStmt},
21122112
{Name: "BenchmarkRows", F: benchmarkRows},
21132113
{Name: "BenchmarkStmtRows", F: benchmarkStmtRows},
2114+
{Name: "BenchmarkExecStep", F: benchmarkExecStep},
2115+
{Name: "BenchmarkQueryStep", F: benchmarkQueryStep},
21142116
}
21152117

21162118
func (db *TestDB) mustExec(sql string, args ...any) sql.Result {
@@ -2568,3 +2570,22 @@ func benchmarkStmtRows(b *testing.B) {
25682570
}
25692571
}
25702572
}
2573+
2574+
var largeSelectStmt = strings.Repeat("select 1;\n", 1_000)
2575+
2576+
func benchmarkExecStep(b *testing.B) {
2577+
for n := 0; n < b.N; n++ {
2578+
if _, err := db.Exec(largeSelectStmt); err != nil {
2579+
b.Fatal(err)
2580+
}
2581+
}
2582+
}
2583+
2584+
func benchmarkQueryStep(b *testing.B) {
2585+
var i int
2586+
for n := 0; n < b.N; n++ {
2587+
if err := db.QueryRow(largeSelectStmt).Scan(&i); err != nil {
2588+
b.Fatal(err)
2589+
}
2590+
}
2591+
}

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