db: turn generated queries array into a simple hash table.

Since we have that functionality, let's use it.  Also, make table
const.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/sql-rewrite.py

@@ -27,6 +27,8 @@ class Rewriter(object):
 
     def rewrite(self, queries):
         for i, q in enumerate(queries):
+            if q['name'] is None:
+                continue
             org = q['query']
             queries[i]['query'] = self.rewrite_single(org)
             eprint("Rewritten statement\n\tfrom {}\n\t  to {}".format(org, q['query']))
@@ -136,10 +138,11 @@ static const struct sqlname_map ${colname}[] = {
 
 % endfor
 
-struct db_query db_${f}_queries[] = {
+const struct db_query db_${f}_queries[] = {
 
 % for elem in queries:
     {
+% if elem['name'] is not None:
          .name = "${elem['name']}",
          .query = "${elem['query']}",
          .placeholders = ${elem['placeholders']},
@@ -147,19 +150,32 @@ struct db_query db_${f}_queries[] = {
 % if elem['colnames'] is not None:
          .colnames = ${elem['colnames']},
          .num_colnames = ARRAY_SIZE(${elem['colnames']}),
+% endif
 % endif
     },
 % endfor
 };
 
-#define DB_${f.upper()}_QUERY_COUNT ${len(queries)}
-
 #endif /* HAVE_${f.upper()} */
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_${f.upper()} */
 """)
 
 
+def queries_htable(queries):
+    # Converts a list of queries into a hash table.
+    tablesize = len(queries) * 2 - 1
+    htable = [{'name': None}] * tablesize
+
+    for q in queries:
+        pos = hash_djb2(q['name']) % tablesize
+        while htable[pos]['name'] is not None:
+            pos = (pos + 1) % tablesize
+        htable[pos] = q
+
+    return htable
+
+
 def extract_queries(pofile):
     # Given a po-file, extract all queries and their associated names, and
     # return them as a list.
@@ -204,7 +220,7 @@ def extract_queries(pofile):
             'readonly': "true" if is_select else "false",
             'colnames': colnames,
         })
-    return colhtables, queries
+    return colhtables, queries_htable(queries)
 
 
 if __name__ == "__main__":

wallet/db.c

@@ -903,12 +903,20 @@ static void db_stmt_free(struct db_stmt *stmt)
 	assert(stmt->inner_stmt == NULL);
 }
 
+/* Matches the hash function used in devtools/sql-rewrite.py */
+static u32 hash_djb2(const char *str)
+{
+	u32 hash = 5381;
+	for (size_t i = 0; str[i]; i++)
+		hash = ((hash << 5) + hash) ^ str[i];
+	return hash;
+}
+
 struct db_stmt *db_prepare_v2_(const char *location, struct db *db,
 				     const char *query_id)
 {
 	struct db_stmt *stmt = tal(db, struct db_stmt);
-	size_t num_slots;
+	size_t num_slots, pos;
-	stmt->query = NULL;
 
 	/* Normalize query_id paths, because unit tests are compiled with this
 	 * prefix. */
@@ -920,14 +928,16 @@ struct db_stmt *db_prepare_v2_(const char *location, struct db *db,
 			 "transaction: %s", location);
 
 	/* Look up the query by its ID */
-	for (size_t i = 0; i < db->config->num_queries; i++) {
+	pos = hash_djb2(query_id) % db->config->query_table_size;
-		if (streq(query_id, db->config->queries[i].name)) {
+	for (;;) {
-			stmt->query = &db->config->queries[i];
+		if (!db->config->query_table[pos].name)
+			fatal("Could not resolve query %s", query_id);
+		if (streq(query_id, db->config->query_table[pos].name)) {
+			stmt->query = &db->config->query_table[pos];
 			break;
 		}
+		pos = (pos + 1) % db->config->query_table_size;
 	}
-	if (stmt->query == NULL)
-		fatal("Could not resolve query %s", query_id);
 
 	num_slots = stmt->query->placeholders;
 	/* Allocate the slots for placeholders/bindings, zeroed next since
@@ -2335,15 +2345,6 @@ const char **db_changes(struct db *db)
 	return db->changes;
 }
 
-/* Matches the hash function used in devtools/sql-rewrite.py */
-static u32 hash_djb2(const char *str)
-{
-	u32 hash = 5381;
-	for (size_t i = 0; str[i]; i++)
-		hash = ((hash << 5) + hash) ^ str[i];
-	return hash;
-}
-
 size_t db_query_colnum(const struct db_stmt *stmt,
 		       const char *colname)
 {

wallet/db_common.h

@@ -84,7 +84,7 @@ struct db_stmt {
 	struct db *db;
 
 	/* Which SQL statement are we trying to execute? */
-	struct db_query *query;
+	const struct db_query *query;
 
 	/* Which parameters are we binding to the statement? */
 	struct db_binding *bindings;
@@ -109,8 +109,8 @@ struct db_stmt {
 
 struct db_config {
 	const char *name;
-	struct db_query *queries;
+	const struct db_query *query_table;
-	size_t num_queries;
+	size_t query_table_size;
 
 	/* Function used to execute a statement that doesn't result in a
 	 * response. */

wallet/db_postgres.c

@@ -275,8 +275,8 @@ static bool db_postgres_vacuum(struct db *db)
 
 struct db_config db_postgres_config = {
     .name = "postgres",
-    .queries = db_postgres_queries,
+    .query_table = db_postgres_queries,
-    .num_queries = DB_POSTGRES_QUERY_COUNT,
+    .query_table_size = ARRAY_SIZE(db_postgres_queries),
     .exec_fn = db_postgres_exec,
     .query_fn = db_postgres_query,
     .step_fn = db_postgres_step,

wallet/db_sqlite3.c

@@ -253,8 +253,8 @@ static bool db_sqlite3_vacuum(struct db *db)
 
 struct db_config db_sqlite3_config = {
 	.name = "sqlite3",
-	.queries = db_sqlite3_queries,
+	.query_table = db_sqlite3_queries,
-	.num_queries = DB_SQLITE3_QUERY_COUNT,
+	.query_table_size = ARRAY_SIZE(db_sqlite3_queries),
 	.exec_fn = &db_sqlite3_exec,
 	.query_fn = &db_sqlite3_query,
 	.step_fn = &db_sqlite3_step,