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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

+72-29
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,7 @@ package sqlite3
3131
#endif
3232
#include <stdlib.h>
3333
#include <string.h>
34+
#include <ctype.h>
3435
3536
#ifdef __CYGWIN__
3637
# include <errno.h>
@@ -79,6 +80,16 @@ _sqlite3_exec(sqlite3* db, const char* pcmd, long long* rowid, long long* change
7980
return rv;
8081
}
8182
83+
static const char *
84+
_trim_leading_spaces(const char *str) {
85+
if (str) {
86+
while (isspace(*str)) {
87+
str++;
88+
}
89+
}
90+
return str;
91+
}
92+
8293
#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY
8394
extern int _sqlite3_step_blocking(sqlite3_stmt *stmt);
8495
extern int _sqlite3_step_row_blocking(sqlite3_stmt* stmt, long long* rowid, long long* changes);
@@ -99,7 +110,11 @@ _sqlite3_step_row_internal(sqlite3_stmt* stmt, long long* rowid, long long* chan
99110
static int
100111
_sqlite3_prepare_v2_internal(sqlite3 *db, const char *zSql, int nBytes, sqlite3_stmt **ppStmt, const char **pzTail)
101112
{
102-
return _sqlite3_prepare_v2_blocking(db, zSql, nBytes, ppStmt, pzTail);
113+
int rv = _sqlite3_prepare_v2_blocking(db, zSql, nBytes, ppStmt, pzTail);
114+
if (pzTail) {
115+
*pzTail = _trim_leading_spaces(*pzTail);
116+
}
117+
return rv;
103118
}
104119
105120
#else
@@ -122,7 +137,11 @@ _sqlite3_step_row_internal(sqlite3_stmt* stmt, long long* rowid, long long* chan
122137
static int
123138
_sqlite3_prepare_v2_internal(sqlite3 *db, const char *zSql, int nBytes, sqlite3_stmt **ppStmt, const char **pzTail)
124139
{
125-
return sqlite3_prepare_v2(db, zSql, nBytes, ppStmt, pzTail);
140+
int rv = sqlite3_prepare_v2(db, zSql, nBytes, ppStmt, pzTail);
141+
if (pzTail) {
142+
*pzTail = _trim_leading_spaces(*pzTail);
143+
}
144+
return rv;
126145
}
127146
#endif
128147
@@ -848,24 +867,32 @@ func (c *SQLiteConn) Exec(query string, args []driver.Value) (driver.Result, err
848867
}
849868

850869
func (c *SQLiteConn) exec(ctx context.Context, query string, args []driver.NamedValue) (driver.Result, error) {
870+
pquery := C.CString(query)
871+
op := pquery // original pointer
872+
defer C.free(unsafe.Pointer(op))
873+
874+
var stmtArgs []driver.NamedValue
875+
var tail *C.char
876+
s := new(SQLiteStmt) // escapes to the heap so reuse it
851877
start := 0
852878
for {
853-
s, err := c.prepare(ctx, query)
854-
if err != nil {
855-
return nil, err
879+
*s = SQLiteStmt{c: c} // reset
880+
rv := C._sqlite3_prepare_v2_internal(c.db, pquery, C.int(-1), &s.s, &tail)
881+
if rv != C.SQLITE_OK {
882+
return nil, c.lastError()
856883
}
884+
857885
var res driver.Result
858-
if s.(*SQLiteStmt).s != nil {
859-
stmtArgs := make([]driver.NamedValue, 0, len(args))
886+
if s.s != nil {
860887
na := s.NumInput()
861888
if len(args)-start < na {
862-
s.Close()
889+
s.finalize()
863890
return nil, fmt.Errorf("not enough args to execute query: want %d got %d", na, len(args))
864891
}
865892
// consume the number of arguments used in the current
866893
// statement and append all named arguments not
867894
// contained therein
868-
stmtArgs = append(stmtArgs, args[start:start+na]...)
895+
stmtArgs = append(stmtArgs[:0], args[start:start+na]...)
869896
for i := range args {
870897
if (i < start || i >= na) && args[i].Name != "" {
871898
stmtArgs = append(stmtArgs, args[i])
@@ -874,23 +901,23 @@ func (c *SQLiteConn) exec(ctx context.Context, query string, args []driver.Named
874901
for i := range stmtArgs {
875902
stmtArgs[i].Ordinal = i + 1
876903
}
877-
res, err = s.(*SQLiteStmt).exec(ctx, stmtArgs)
904+
var err error
905+
res, err = s.exec(ctx, stmtArgs)
878906
if err != nil && err != driver.ErrSkip {
879-
s.Close()
907+
s.finalize()
880908
return nil, err
881909
}
882910
start += na
883911
}
884-
tail := s.(*SQLiteStmt).t
885-
s.Close()
886-
if tail == "" {
912+
s.finalize()
913+
if tail == nil || *tail == '\000' {
887914
if res == nil {
888915
// https://github.com/mattn/go-sqlite3/issues/963
889916
res = &SQLiteResult{0, 0}
890917
}
891918
return res, nil
892919
}
893-
query = tail
920+
pquery = tail
894921
}
895922
}
896923

@@ -907,22 +934,29 @@ func (c *SQLiteConn) Query(query string, args []driver.Value) (driver.Rows, erro
907934
}
908935

909936
func (c *SQLiteConn) query(ctx context.Context, query string, args []driver.NamedValue) (driver.Rows, error) {
937+
pquery := C.CString(query)
938+
op := pquery // original pointer
939+
defer C.free(unsafe.Pointer(op))
940+
941+
var stmtArgs []driver.NamedValue
942+
var tail *C.char
943+
s := new(SQLiteStmt) // escapes to the heap so reuse it
910944
start := 0
911945
for {
912-
stmtArgs := make([]driver.NamedValue, 0, len(args))
913-
s, err := c.prepare(ctx, query)
914-
if err != nil {
915-
return nil, err
946+
*s = SQLiteStmt{c: c, cls: true} // reset
947+
rv := C._sqlite3_prepare_v2_internal(c.db, pquery, C.int(-1), &s.s, &tail)
948+
if rv != C.SQLITE_OK {
949+
return nil, c.lastError()
916950
}
917-
s.(*SQLiteStmt).cls = true
951+
918952
na := s.NumInput()
919953
if len(args)-start < na {
920954
return nil, fmt.Errorf("not enough args to execute query: want %d got %d", na, len(args)-start)
921955
}
922956
// consume the number of arguments used in the current
923957
// statement and append all named arguments not contained
924958
// therein
925-
stmtArgs = append(stmtArgs, args[start:start+na]...)
959+
stmtArgs = append(stmtArgs[:0], args[start:start+na]...)
926960
for i := range args {
927961
if (i < start || i >= na) && args[i].Name != "" {
928962
stmtArgs = append(stmtArgs, args[i])
@@ -931,19 +965,18 @@ func (c *SQLiteConn) query(ctx context.Context, query string, args []driver.Name
931965
for i := range stmtArgs {
932966
stmtArgs[i].Ordinal = i + 1
933967
}
934-
rows, err := s.(*SQLiteStmt).query(ctx, stmtArgs)
968+
rows, err := s.query(ctx, stmtArgs)
935969
if err != nil && err != driver.ErrSkip {
936-
s.Close()
970+
s.finalize()
937971
return rows, err
938972
}
939973
start += na
940-
tail := s.(*SQLiteStmt).t
941-
if tail == "" {
974+
if tail == nil || *tail == '\000' {
942975
return rows, nil
943976
}
944977
rows.Close()
945-
s.Close()
946-
query = tail
978+
s.finalize()
979+
pquery = tail
947980
}
948981
}
949982

@@ -1805,8 +1838,11 @@ func (c *SQLiteConn) prepare(ctx context.Context, query string) (driver.Stmt, er
18051838
return nil, c.lastError()
18061839
}
18071840
var t string
1808-
if tail != nil && *tail != '\000' {
1809-
t = strings.TrimSpace(C.GoString(tail))
1841+
if tail != nil && *tail != 0 {
1842+
n := int(uintptr(unsafe.Pointer(tail))) - int(uintptr(unsafe.Pointer(pquery)))
1843+
if 0 <= n && n < len(query) {
1844+
t = strings.TrimSpace(query[n:])
1845+
}
18101846
}
18111847
ss := &SQLiteStmt{c: c, s: s, t: t}
18121848
runtime.SetFinalizer(ss, (*SQLiteStmt).Close)
@@ -1899,6 +1935,13 @@ func (s *SQLiteStmt) Close() error {
18991935
return nil
19001936
}
19011937

1938+
func (s *SQLiteStmt) finalize() {
1939+
if s.s != nil {
1940+
C.sqlite3_finalize(s.s)
1941+
s.s = nil
1942+
}
1943+
}
1944+
19021945
// NumInput return a number of parameters.
19031946
func (s *SQLiteStmt) NumInput() int {
19041947
return int(C.sqlite3_bind_parameter_count(s.s))

‎sqlite3_test.go

+21
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 ...interface{}) 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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