JS: change the default OPFS VFS journal mode from PERSIST to DELETE, as DELETE is faster in current browsers.

FossilOrigin-Name: a061a43e36b8f3cb7c465fd2e54cfcd9dceb07e232ee78602bbdd1818acd05ea

ext/wasm/api/sqlite3-vfs-opfs.c-pp.js

@@ -298,6 +298,7 @@ const installOpfsVfs = function callee(options){
        lock contention to free up.
     */
     state.asyncIdleWaitTime = 150;
+
     /**
        Whether the async counterpart should log exceptions to
        the serialization channel. That produces a great deal of
@@ -1186,19 +1187,23 @@ const installOpfsVfs = function callee(options){
              contention. */
           sqlite3.capi.sqlite3_busy_timeout(oo1Db, 10000);
           sqlite3.capi.sqlite3_exec(oo1Db, [
-            /* Truncate journal mode is faster than delete for
-               this vfs, per speedtest1. That gap seems to have closed with
-               Chrome version 108 or 109, but "persist" is very roughly 5-6%
-               faster than truncate in initial tests.
+            /* As of July 2023, the PERSIST journal mode on OPFS is
+               somewhat slower than DELETE or TRUNCATE (it was faster
+               before Chrome version 108 or 109). TRUNCATE and DELETE
+               have very similar performance on OPFS.
 
-               For later analysis: Roy Hashimoto notes that TRUNCATE
-               and PERSIST modes may decrease OPFS concurrency because
-               multiple connections can open the journal file in those
-               modes:
+               Roy Hashimoto notes that TRUNCATE and PERSIST modes may
+               decrease OPFS concurrency because multiple connections
+               can open the journal file in those modes:
 
                https://github.com/rhashimoto/wa-sqlite/issues/68
+
+               Given that, and the fact that testing has not revealed
+               any appreciable difference between performance of
+               TRUNCATE and DELETE modes on OPFS, we currently (as of
+               2023-07-13) default to DELETE mode.
             */
-            "pragma journal_mode=persist;",
+            "pragma journal_mode=DELETE;",
             /*
               This vfs benefits hugely from cache on moderate/large
               speedtest1 --size 50 and --size 100 workloads. We

manifest

@@ -1,5 +1,5 @@
-C Remove\sobsolete\sext/wasm/api/sqlite3-wasi.h.
-D 2023-07-13T01:48:53.998
+C JS:\schange\sthe\sdefault\sOPFS\sVFS\sjournal\smode\sfrom\sPERSIST\sto\sDELETE,\sas\sDELETE\sis\sfaster\sin\scurrent\sbrowsers.
+D 2023-07-13T01:51:16.511
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 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

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