libstore: add SQLite::Settings struct for explicit configuration

src/libexpr/eval-cache.cc

@@ -75,7 +75,7 @@ struct AttrDb
 
         auto dbPath = cacheDir / (fingerprint.to_string(HashFormat::Base16, false) + ".sqlite");
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         state->db.isCache();
         state->db.exec(schema);
 

src/libfetchers/cache.cc

@@ -41,7 +41,7 @@ struct CacheImpl : Cache
         auto dbPath = (getCacheDir() / "fetcher-cache-v4.sqlite").string();
         createDirs(dirOf(dbPath));
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         state->db.isCache();
         state->db.exec(schema);
 

src/libstore-tests/nar-info-disk-cache.cc

@@ -2,6 +2,7 @@
 
 #include <gtest/gtest.h>
 #include <rapidcheck/gtest.h>
+#include "nix/store/globals.hh"
 #include "nix/store/sqlite.hh"
 #include <sqlite3.h>
 
@@ -48,7 +49,7 @@ TEST(NarInfoDiskCacheImpl, create_and_read)
 
         // We're going to pay special attention to the id field because we had a bug
         // that changed it.
-        db = SQLite(dbPath);
+        db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         getIds.create(db, "select id from BinaryCaches where url = 'http://foo'");
 
         {

src/libstore/include/nix/store/sqlite.hh

@@ -42,7 +42,13 @@ struct SQLite
 
     SQLite() {}
 
-    SQLite(const std::filesystem::path & path, SQLiteOpenMode mode = SQLiteOpenMode::Normal);
+    struct Settings
+    {
+        SQLiteOpenMode mode = SQLiteOpenMode::Normal;
+        bool useWAL;
+    };
+
+    SQLite(const std::filesystem::path & path, Settings && settings);
     SQLite(const SQLite & from) = delete;
     SQLite & operator=(const SQLite & from) = delete;
 

src/libstore/local-store.cc

@@ -481,7 +481,7 @@ void LocalStore::openDB(State & state, bool create)
     auto openMode = config->readOnly ? SQLiteOpenMode::Immutable
                     : create         ? SQLiteOpenMode::Normal
                                      : SQLiteOpenMode::NoCreate;
-    state.db = SQLite(std::filesystem::path(dbDir) / "db.sqlite", openMode);
+    state.db = SQLite(std::filesystem::path(dbDir) / "db.sqlite", {.mode = openMode, .useWAL = settings.useSQLiteWAL});
 
 #ifdef __CYGWIN__
     /* The cygwin version of sqlite3 has a patch which calls

src/libstore/nar-info-disk-cache.cc

@@ -92,7 +92,7 @@ class NarInfoDiskCacheImpl : public NarInfoDiskCache
 
         createDirs(dirOf(dbPath));
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
 
         state->db.isCache();
 

src/libstore/sqlite.cc

@@ -62,7 +62,7 @@ static void traceSQL(void * x, const char * sql)
     notice("SQL<[%1%]>", sql);
 };
 
-SQLite::SQLite(const std::filesystem::path & path, SQLiteOpenMode mode)
+SQLite::SQLite(const std::filesystem::path & path, Settings && settings)
 {
     // Work around a ZFS issue where SQLite's truncate() call on
     // db.sqlite-shm can randomly take up to a few seconds. See
@@ -89,10 +89,10 @@ SQLite::SQLite(const std::filesystem::path & path, SQLiteOpenMode mode)
     // useSQLiteWAL also indicates what virtual file system we need.  Using
     // `unix-dotfile` is needed on NFS file systems and on Windows' Subsystem
     // for Linux (WSL) where useSQLiteWAL should be false by default.
-    const char * vfs = settings.useSQLiteWAL ? 0 : "unix-dotfile";
-    bool immutable = mode == SQLiteOpenMode::Immutable;
+    const char * vfs = settings.useWAL ? 0 : "unix-dotfile";
+    bool immutable = settings.mode == SQLiteOpenMode::Immutable;
     int flags = immutable ? SQLITE_OPEN_READONLY : SQLITE_OPEN_READWRITE;
-    if (mode == SQLiteOpenMode::Normal)
+    if (settings.mode == SQLiteOpenMode::Normal)
         flags |= SQLITE_OPEN_CREATE;
     auto uri = "file:" + percentEncode(path.string()) + "?immutable=" + (immutable ? "1" : "0");
     int ret = sqlite3_open_v2(uri.c_str(), &db, SQLITE_OPEN_URI | flags, vfs);