Index: ext/wasm/api/sqlite3-api-opfs.js
==================================================================
--- ext/wasm/api/sqlite3-api-opfs.js
+++ ext/wasm/api/sqlite3-api-opfs.js
@@ -465,13 +465,15 @@
       };
 
       /**
          Returns an array of the deserialized state stored by the most
          recent serialize() operation (from from this thread or the
-         counterpart thread), or null if the serialization buffer is empty.
+         counterpart thread), or null if the serialization buffer is
+         empty.  If passed a truthy argument, the serialization buffer
+         is cleared after deserialization.
       */
-      state.s11n.deserialize = function(){
+      state.s11n.deserialize = function(clear=false){
         ++metrics.s11n.deserialize.count;
         const t = performance.now();
         const argc = viewU8[0];
         const rc = argc ? [] : null;
         if(argc){
@@ -492,10 +494,11 @@
               offset += n;
             }
             rc.push(v);
           }
         }
+        if(clear) viewU8[0] = 0;
         //log("deserialize:",argc, rc);
         metrics.s11n.deserialize.time += performance.now() - t;
         return rc;
       };
 

Index: ext/wasm/api/sqlite3-opfs-async-proxy.js
==================================================================
--- ext/wasm/api/sqlite3-opfs-async-proxy.js
+++ ext/wasm/api/sqlite3-opfs-async-proxy.js
@@ -42,10 +42,11 @@
 /**
    Will hold state copied to this object from the syncronous side of
    this API.
 */
 const state = Object.create(null);
+
 /**
    verbose:
 
    0 = no logging output
    1 = only errors
@@ -94,17 +95,31 @@
               "approx",w,"ms spent waiting on OPFS APIs.");
   console.log("Serialization metrics:",metrics.s11n);
 };
 
 /**
-   Map of sqlite3_file pointers (integers) to metadata related to a
-   given OPFS file handles. The pointers are, in this side of the
-   interface, opaque file handle IDs provided by the synchronous
-   part of this constellation. Each value is an object with a structure
-   demonstrated in the xOpen() impl.
+   __openFiles is a map of sqlite3_file pointers (integers) to
+   metadata related to a given OPFS file handles. The pointers are, in
+   this side of the interface, opaque file handle IDs provided by the
+   synchronous part of this constellation. Each value is an object
+   with a structure demonstrated in the xOpen() impl.
 */
 const __openFiles = Object.create(null);
+/**
+   __autoLocks is a Set of sqlite3_file pointers (integers) which were
+   "auto-locked".  i.e. those for which we obtained a sync access
+   handle without an explicit xLock() call. Such locks will be
+   released during db connection idle time, whereas a sync access
+   handle obtained via xLock(), or subsequently xLock()'d after
+   auto-acquisition, will not be released until xUnlock() is called.
+
+   Maintenance reminder: if we relinquish auto-locks at the end of the
+   operation which acquires them, we pay a massive performance
+   penalty: speedtest1 benchmarks take up to 4x as long. By delaying
+   the lock release until idle time, the hit is negligible.
+*/
+const __autoLocks = new Set();
 
 /**
    Expects an OPFS file path. It gets resolved, such that ".."
    components are properly expanded, and returned. If the 2nd arg is
    true, the result is returned as an array of path elements, else an
@@ -189,10 +204,14 @@
               "ms and trying again.",fh.filenameAbs,e);
         Atomics.wait(state.sabOPView, state.opIds.retry, 0, ms);
       }
     }
     log("Got sync handle for",fh.filenameAbs,'in',performance.now() - t,'ms');
+    if(!fh.xLock){
+      __autoLocks.add(fh.fid);
+      log("Auto-locked",fh.fid,fh.filenameAbs);
+    }
   }
   return fh.syncHandle;
 };
 
 /**
@@ -208,13 +227,33 @@
 const closeSyncHandle = async (fh)=>{
   if(fh.syncHandle){
     log("Closing sync handle for",fh.filenameAbs);
     const h = fh.syncHandle;
     delete fh.syncHandle;
+    delete fh.xLock;
+    __autoLocks.delete(fh.fid);
     return h.close();
   }
 };
+
+/**
+   A proxy for closeSyncHandle() which is guaranteed to not throw.
+
+   This function is part of a lock/unlock step in functions which
+   require a sync access handle but may be called without xLock()
+   having been called first. Such calls need to release that
+   handle to avoid locking the file for all of time. This is an
+   _attempt_ at reducing cross-tab contention but it may prove
+   to be more of a problem than a solution and may need to be
+   removed.
+*/
+const closeSyncHandleNoThrow = async (fh)=>{
+  try{await closeSyncHandle(fh)}
+  catch(e){
+    warn("closeSyncHandleNoThrow() ignoring:",e,fh);
+  }
+};
 
 /**
    Stores the given value at state.sabOPView[state.opIds.rc] and then
    Atomics.notify()'s it.
 */
@@ -340,13 +379,14 @@
     mTimeEnd();
   },
   xClose: async function(fid/*sqlite3_file pointer*/){
     const opName = 'xClose';
     mTimeStart(opName);
+    __autoLocks.delete(fid);
     const fh = __openFiles[fid];
     let rc = 0;
-    wTimeStart('xClose');
+    wTimeStart(opName);
     if(fh){
       delete __openFiles[fid];
       await closeSyncHandle(fh);
       if(fh.deleteOnClose){
         try{ await fh.dirHandle.removeEntry(fh.filenamePart) }
@@ -420,16 +460,21 @@
   xLock: async function(fid/*sqlite3_file pointer*/,
                         lockType/*SQLITE_LOCK_...*/){
     mTimeStart('xLock');
     const fh = __openFiles[fid];
     let rc = 0;
+    const oldLockType = fh.xLock;
+    fh.xLock = lockType;
     if( !fh.syncHandle ){
       wTimeStart('xLock');
-      try { await getSyncHandle(fh) }
-      catch(e){
+      try {
+        await getSyncHandle(fh);
+        __autoLocks.delete(fid);
+      }catch(e){
         state.s11n.storeException(1,e);
         rc = state.sq3Codes.SQLITE_IOERR_LOCK;
+        fh.xLock = oldLockType;
       }
       wTimeEnd();
     }
     storeAndNotify('xLock',rc);
     mTimeEnd();
@@ -459,10 +504,11 @@
          object, but only for certain cases and it's unclear why it
          places that limitation on it.
       */
       wTimeEnd();
       __openFiles[fid] = Object.assign(Object.create(null),{
+        fid: fid,
         filenameAbs: filename,
         filenamePart: filenamePart,
         dirHandle: hDir,
         fileHandle: hFile,
         sabView: state.sabFileBufView,
@@ -608,11 +654,11 @@
       case TypeIds.boolean.id: return TypeIds.boolean;
       case TypeIds.string.id: return TypeIds.string;
       default: toss("Invalid type ID:",tid);
     }
   };
-  state.s11n.deserialize = function(){
+  state.s11n.deserialize = function(clear=false){
     ++metrics.s11n.deserialize.count;
     const t = performance.now();
     const argc = viewU8[0];
     const rc = argc ? [] : null;
     if(argc){
@@ -633,10 +679,11 @@
           offset += n;
         }
         rc.push(v);
       }
     }
+    if(clear) viewU8[0] = 0;
     //log("deserialize:",argc, rc);
     metrics.s11n.deserialize.time += performance.now() - t;
     return rc;
   };
   state.s11n.serialize = function(...args){
@@ -699,25 +746,34 @@
   /**
      waitTime is how long (ms) to wait for each Atomics.wait().
      We need to wake up periodically to give the thread a chance
      to do other things.
   */
-  const waitTime = 1000;
+  const waitTime = 500;
   while(!flagAsyncShutdown){
     try {
       if('timed-out'===Atomics.wait(
         state.sabOPView, state.opIds.whichOp, 0, waitTime
       )){
+        if(__autoLocks.size){
+          /* Release all auto-locks. */
+          for(const fid of __autoLocks){
+            const fh = __openFiles[fid];
+            await closeSyncHandleNoThrow(fh);
+            log("Auto-unlocked",fid,fh.filenameAbs);
+          }
+        }
         continue;
       }
       const opId = Atomics.load(state.sabOPView, state.opIds.whichOp);
       Atomics.store(state.sabOPView, state.opIds.whichOp, 0);
       const hnd = opHandlers[opId] ?? toss("No waitLoop handler for whichOp #",opId);
-      const args = state.s11n.deserialize() || [];
-      state.s11n.serialize(/* clear s11n to keep the caller from
-                              confusing this with an exception string
-                              written by the upcoming operation */);
+      const args = state.s11n.deserialize(
+        true /* clear s11n to keep the caller from confusing this with
+                an exception string written by the upcoming
+                operation */
+      ) || [];
       //warn("waitLoop() whichOp =",opId, hnd, args);
       if(hnd.f) await hnd.f(...args);
       else error("Missing callback for opId",opId);
     }catch(e){
       error('in waitLoop():',e);

Index: ext/wasm/module-symbols.html
==================================================================
--- ext/wasm/module-symbols.html
+++ ext/wasm/module-symbols.html
@@ -187,11 +187,11 @@
       of <code>sqlite3.wasm</code>...
     </p>
     <div id='list-compile-options' class='pseudolist wide2'></div>
 
   </div><!-- .initially-hidden -->
-  <script src="jswasm/sqlite3.js">/* This tag MUST be in side the
+  <script src="jswasm/sqlite3.js">/* This tag MUST be inside the
   fossil-doc block so that this part can work without modification in
   the wasm docs repo.  */</script>
   <script>(async function(){
     const eNew = (tag,parent)=>{
         const e = document.createElement(tag);

Index: ext/wasm/speedtest1-worker.html
==================================================================
--- ext/wasm/speedtest1-worker.html
+++ ext/wasm/speedtest1-worker.html
@@ -167,21 +167,24 @@
         else if(str.length>len) return str.substr(0,len);
         const a = []; a.length = len - str.length;
         return str+a.join('&nbsp;');
     };
 
-    const W = new Worker("speedtest1-worker.js?sqlite3.dir=jswasm");
+    const urlParams = new URL(self.location.href).searchParams;
+    const W = new Worker(
+        "speedtest1-worker.js?sqlite3.dir=jswasm"+
+            (urlParams.has('opfs-verbose') ? '&opfs-verbose' : '')
+    );
     const mPost = function(msgType,payload){
         W.postMessage({type: msgType, data: payload});
     };
 
     const eFlags = E('#select-flags');
     const eSelectedFlags = E('#toolbar-selected-flags');
     const eLinkMainThread = E('#link-main-thread');
     const eLinkWasmfs = E('#link-wasmfs');
     const eLinkKvvfs = E('#link-kvvfs');
-    const urlParams = new URL(self.location.href).searchParams;
     const getSelectedFlags = ()=>{
         const f = Array.prototype.map.call(eFlags.selectedOptions, (v)=>v.value);
         [
             'size', 'vfs', 'journal', 'cachesize'
         ].forEach(function(k){