Created
July 30, 2013 20:05
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Retrieve `matchinfo` from FTS4 table on SQLite.
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package main | |
import ( | |
"bytes" | |
"database/sql" | |
"encoding/binary" | |
_ "github.com/mattn/go-sqlite3" | |
"log" | |
) | |
func loadDB() *sql.DB { | |
db, err := sql.Open("sqlite3", ":memory:") | |
if err != nil { | |
log.Fatal(err) | |
} | |
var sqliteVersion string | |
err = db.QueryRow("select sqlite_version()").Scan(&sqliteVersion) | |
if err != nil { | |
log.Fatal(err) | |
} | |
log.Println("SQLite version:", sqliteVersion) | |
log.Println("creating FTS index...") | |
_, err = db.Exec("CREATE VIRTUAL TABLE dict USING fts4(key, entry)") | |
if err != nil { | |
log.Fatal(err) | |
} | |
insertStmt, err := db.Prepare("INSERT INTO dict(key, entry) VALUES(?, ?)") | |
if err != nil { | |
log.Fatal(err) | |
} | |
defer insertStmt.Close() | |
dict := map[string]string{ | |
"Russia": "Moscow", | |
"Poland": "Warsaw", | |
} | |
for key, entry := range dict { | |
insertStmt.Exec(key, entry) | |
} | |
log.Printf("indexed %d entries\n", len(dict)) | |
return db | |
} | |
type MatchInfo struct { | |
P, C uint32 | |
X []uint32 | |
} | |
func (mi *MatchInfo) Read(b []byte) { | |
buf := bytes.NewBuffer(b) | |
binary.Read(buf, binary.LittleEndian, &mi.P) | |
binary.Read(buf, binary.LittleEndian, &mi.C) | |
mi.X = make([]uint32, 3*mi.P*mi.C) | |
binary.Read(buf, binary.LittleEndian, &mi.X) | |
} | |
func search(db *sql.DB, term string) map[int]MatchInfo { | |
rows, err := db.Query("SELECT docid, matchinfo(dict) FROM dict WHERE entry MATCH ?", term) | |
if err != nil { | |
log.Fatal(err) | |
} | |
defer rows.Close() | |
results := make(map[int]MatchInfo) | |
for rows.Next() { | |
var ( | |
docid int | |
miBytes *[]byte | |
mi MatchInfo | |
) | |
if err := rows.Scan(&docid, &miBytes); err != nil { | |
log.Fatal(err) | |
} | |
mi.Read(*miBytes) | |
//log.Println("****", docid, mi) | |
results[docid] = mi | |
} | |
return results | |
} | |
func main() { | |
db := loadDB() | |
defer db.Close() | |
log.Println("results:", search(db, "Warsaw")) | |
} |
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I observe
segmentation violation
whendb.Close()
is called. Tested in two environments:Env 1:
Env 2: