diff --git a/ext/wasm/api/sqlite3-api-opfs.js b/ext/wasm/api/sqlite3-api-opfs.js
index dd61ee0a26..1f50b4631a 100644
--- a/ext/wasm/api/sqlite3-api-opfs.js
+++ b/ext/wasm/api/sqlite3-api-opfs.js
@@ -152,6 +152,7 @@ sqlite3.installOpfsVfs = function callee(asyncProxyUri = callee.defaultProxyUri)
                     "metrics for",self.location.href,":",metrics,
                     "\nTotal of",n,"op(s) for",t,
                     "ms (incl. "+w+" ms of waiting on the async side)");
+        console.log("Serialization metrics:",JSON.stringify(metrics.s11n,0,2));
       },
       reset: function(){
         let k;
@@ -159,6 +160,11 @@ sqlite3.installOpfsVfs = function callee(asyncProxyUri = callee.defaultProxyUri)
         for(k in state.opIds){
           r(metrics[k] = Object.create(null));
         }
+        let s = metrics.s11n = Object.create(null);
+        s = s.serialize = Object.create(null);
+        s.count = s.time = 0;
+        s = metrics.s11n.deserialize = Object.create(null);
+        s.count = s.time = 0;
         //[ // timed routines which are not in state.opIds
         //  'xFileControl'
         //].forEach((k)=>r(metrics[k] = Object.create(null)));
@@ -314,56 +320,115 @@ sqlite3.installOpfsVfs = function callee(asyncProxyUri = callee.defaultProxyUri)
     };
 
     const initS11n = ()=>{
-      // Achtung: this code is 100% duplicated in the other half of this proxy!
+      /**
+         ACHTUNG: this code is 100% duplicated in the other half of
+         this proxy!
+
+         Historical note: this impl was initially about 5% this size by using
+         using JSON.stringify/parse(), but using fit-to-purpose serialization
+         saves considerable runtime.
+      */
       if(state.s11n) return state.s11n;
-      const jsonDecoder = new TextDecoder(),
-            jsonEncoder = new TextEncoder('utf-8'),
-            viewSz = new DataView(state.sabIO, state.sabS11nOffset, 4),
-            viewJson = new Uint8Array(state.sabIO, state.sabS11nOffset+4, state.sabS11nSize-4);
+      const textDecoder = new TextDecoder(),
+      textEncoder = new TextEncoder('utf-8'),
+      viewU8 = new Uint8Array(state.sabIO, state.sabS11nOffset, state.sabS11nSize),
+      viewDV = new DataView(state.sabIO, state.sabS11nOffset, state.sabS11nSize);
       state.s11n = Object.create(null);
+      const TypeIds = Object.create(null);
+      TypeIds.number  = { id: 1, size: 8, getter: 'getFloat64', setter: 'setFloat64' };
+      TypeIds.bigint  = { id: 2, size: 8, getter: 'getBigInt64', setter: 'setBigInt64' };
+      TypeIds.boolean = { id: 3, size: 4, getter: 'getInt32', setter: 'setInt32' };
+      TypeIds.string =  { id: 4 };
+      const getTypeId = (v)=>{
+        return TypeIds[typeof v] || toss("This value type cannot be serialized.",v);
+      };
+      const getTypeIdById = (tid)=>{
+        switch(tid){
+        case TypeIds.number.id: return TypeIds.number;
+        case TypeIds.bigint.id: return TypeIds.bigint;
+        case TypeIds.boolean.id: return TypeIds.boolean;
+        case TypeIds.string.id: return TypeIds.string;
+        default: toss("Invalid type ID:",tid);
+        }
+      };
       /**
          Returns an array of the state serialized by the most recent
          serialize() operation (here or in the counterpart thread), or
          null if the serialization buffer is empty.
       */
       state.s11n.deserialize = function(){
-        const sz = viewSz.getInt32(0, state.littleEndian);
-        const json = sz ? jsonDecoder.decode(
-          viewJson.slice(0, sz)
-          /* slice() (copy) needed, instead of subarray() (reference),
-             because TextDecoder throws if asked to decode from an
-             SAB. */
-        ) : null;
-        return JSON.parse(json);
-      }
+        ++metrics.s11n.deserialize.count;
+        const t = performance.now();
+        let rc = null;
+        const argc = viewU8[0];
+        if(argc){
+          rc = [];
+          let offset = 1, i, n, v, typeIds = [];
+          for(i = 0; i < argc; ++i, ++offset){
+            typeIds.push(getTypeIdById(viewU8[offset]));
+          }
+          for(i = 0; i < argc; ++i){
+            const t = typeIds[i];
+            if(t.getter){
+              v = viewDV[t.getter](offset, state.littleEndian);
+              offset += t.size;
+            }else{
+              n = viewDV.getInt32(offset, state.littleEndian);
+              offset += 4;
+              v = textDecoder.decode(viewU8.slice(offset, offset+n));
+              offset += n;
+            }
+            rc.push(v);
+          }
+        }
+        //log("deserialize:",argc, rc);
+        metrics.s11n.deserialize.time += performance.now() - t;
+        return rc;
+      };
       /**
          Serializes all arguments to the shared buffer for consumption
-         by the counterpart thread. This impl currently uses JSON for
-         serialization for simplicy of implementation, but if that
-         proves imperformant then a lower-level approach will be
-         created.
+         by the counterpart thread.
 
-         If passed "too much data" (more that the shared buffer size
-         it will either throw or truncate the data (not certain
-         which)). This routine is only intended for serializing OPFS
-         VFS arguments and (in at least one special case) result
-         values, and the buffer is sized to be able to comfortably
-         handle those.
+         This routine is only intended for serializing OPFS VFS
+         arguments and (in at least one special case) result values,
+         and the buffer is sized to be able to comfortably handle
+         those.
 
          If passed no arguments then it zeroes out the serialization
          state.
       */
       state.s11n.serialize = function(...args){
+        ++metrics.s11n.serialize.count;
+        const t = performance.now();
         if(args.length){
-          const json = jsonEncoder.encode(JSON.stringify(args));
-          viewSz.setInt32(0, json.byteLength, state.littleEndian);
-          viewJson.set(json);
+          //log("serialize():",args);
+          let i = 0, offset = 1, typeIds = [];
+          viewU8[0] = args.length & 0xff;
+          for(; i < args.length; ++i, ++offset){
+            typeIds.push(getTypeId(args[i]));
+            viewU8[offset] = typeIds[i].id;
+          }
+          for(i = 0; i < args.length; ++i) {
+            const t = typeIds[i];
+            if(t.setter){
+              viewDV[t.setter](offset, args[i], state.littleEndian);
+              offset += t.size;
+            }else{
+              const s = textEncoder.encode(args[i]);
+              viewDV.setInt32(offset, s.byteLength, state.littleEndian);
+              offset += 4;
+              viewU8.set(s, offset);
+              offset += s.byteLength;
+            }
+          }
+          //log("serialize() result:",viewU8.slice(0,offset));
         }else{
-          viewSz.setInt32(0, 0, state.littleEndian);
+          viewU8[0] = 0;
         }
+        metrics.s11n.serialize.time += performance.now() - t;
       };
       return state.s11n;
-    };
+    }/*initS11n()*/;
 
     /**
        Generates a random ASCII string len characters long, intended for
@@ -762,7 +827,7 @@ sqlite3.installOpfsVfs = function callee(asyncProxyUri = callee.defaultProxyUri)
         //| capi.SQLITE_OPEN_DELETEONCLOSE
               | capi.SQLITE_OPEN_MAIN_DB;
         const pOut = wasm.scopedAlloc(8);
-        const dbFile = "/sanity/check/file";
+        const dbFile = "/sanity/check/file"+randomFilename(8);
         const zDbFile = wasm.scopedAllocCString(dbFile);
         let rc;
         vfsSyncWrappers.xAccess(opfsVfs.pointer, zDbFile, 0, pOut);
diff --git a/ext/wasm/sqlite3-opfs-async-proxy.js b/ext/wasm/sqlite3-opfs-async-proxy.js
index 6caf21597a..7c5e8430b6 100644
--- a/ext/wasm/sqlite3-opfs-async-proxy.js
+++ b/ext/wasm/sqlite3-opfs-async-proxy.js
@@ -67,6 +67,11 @@ metrics.reset = ()=>{
   for(k in state.opIds){
     r(metrics[k] = Object.create(null));
   }
+  let s = metrics.s11n = Object.create(null);
+  s = s.serialize = Object.create(null);
+  s.count = s.time = 0;
+  s = metrics.s11n.deserialize = Object.create(null);
+  s.count = s.time = 0;
 };
 metrics.dump = ()=>{
   let k, n = 0, t = 0, w = 0;
@@ -83,6 +88,7 @@ metrics.dump = ()=>{
               /*dev console can't expand this object!*/,
               "\nTotal of",n,"op(s) for",t,"ms",
               "approx",w,"ms spent waiting on OPFS APIs.");
+  console.log("Serialization metrics:",JSON.stringify(metrics.s11n,0,2));
 };
 
 warn("This file is very much experimental and under construction.",
@@ -408,55 +414,118 @@ const vfsAsyncImpls = {
 
 const initS11n = ()=>{
   // Achtung: this code is 100% duplicated in the other half of this proxy!
+
+  /**
+     Historical note: this impl was initially about 1% this size by using
+     using JSON.stringify/parse(), but using fit-to-purpose serialization
+     saves considerable runtime.
+  */
+
   if(state.s11n) return state.s11n;
-  const jsonDecoder = new TextDecoder(),
-        jsonEncoder = new TextEncoder('utf-8'),
-        viewSz = new DataView(state.sabIO, state.sabS11nOffset, 4),
-        viewJson = new Uint8Array(state.sabIO, state.sabS11nOffset+4, state.sabS11nSize-4);
+  const textDecoder = new TextDecoder(),
+  textEncoder = new TextEncoder('utf-8'),
+  viewU8 = new Uint8Array(state.sabIO, state.sabS11nOffset, state.sabS11nSize),
+  viewDV = new DataView(state.sabIO, state.sabS11nOffset, state.sabS11nSize);
   state.s11n = Object.create(null);
+
+  const TypeIds = Object.create(null);
+  TypeIds.number  = { id: 1, size: 8, getter: 'getFloat64', setter: 'setFloat64' };
+  TypeIds.bigint  = { id: 2, size: 8, getter: 'getBigInt64', setter: 'setBigInt64' };
+  TypeIds.boolean = { id: 3, size: 4, getter: 'getInt32', setter: 'setInt32' };
+  TypeIds.string =  { id: 4 };
+
+  const getTypeId = (v)=>{
+    return TypeIds[typeof v] || toss("This value type cannot be serialized.",v);
+  };
+  const getTypeIdById = (tid)=>{
+    switch(tid){
+    case TypeIds.number.id: return TypeIds.number;
+    case TypeIds.bigint.id: return TypeIds.bigint;
+    case TypeIds.boolean.id: return TypeIds.boolean;
+    case TypeIds.string.id: return TypeIds.string;
+    default: toss("Invalid type ID:",tid);
+    }
+  };
+
   /**
      Returns an array of the state serialized by the most recent
      serialize() operation (here or in the counterpart thread), or
      null if the serialization buffer is empty.
   */
   state.s11n.deserialize = function(){
-    const sz = viewSz.getInt32(0, state.littleEndian);
-    const json = sz ? jsonDecoder.decode(
-      viewJson.slice(0, sz)
-      /* slice() (copy) needed, instead of subarray() (reference),
-         because TextDecoder throws if asked to decode from an
-         SAB. */
-    ) : null;
-    return JSON.parse(json);
-  }
+    ++metrics.s11n.deserialize.count;
+    const t = performance.now();
+    let rc = null;
+    const argc = viewU8[0];
+    if(argc){
+      rc = [];
+      let offset = 1, i, n, v, typeIds = [];
+      for(i = 0; i < argc; ++i, ++offset){
+        typeIds.push(getTypeIdById(viewU8[offset]));
+      }
+      for(i = 0; i < argc; ++i){
+        const t = typeIds[i];
+        if(t.getter){
+          v = viewDV[t.getter](offset, state.littleEndian);
+          offset += t.size;
+        }else{
+          n = viewDV.getInt32(offset, state.littleEndian);
+          offset += 4;
+          v = textDecoder.decode(viewU8.slice(offset, offset+n));
+          offset += n;
+        }
+        rc.push(v);
+      }
+    }
+    //log("deserialize:",argc, rc);
+    metrics.s11n.deserialize.time += performance.now() - t;
+    return rc;
+  };
+
   /**
      Serializes all arguments to the shared buffer for consumption
-     by the counterpart thread. This impl currently uses JSON for
-     serialization for simplicy of implementation, but if that
-     proves imperformant then a lower-level approach will be
-     created.
+     by the counterpart thread.
 
-     If passed "too much data" (more that the shared buffer size
-     it will either throw or truncate the data (not certain
-     which)). This routine is only intended for serializing OPFS
-     VFS arguments and (in at least one special case) result
-     values, and the buffer is sized to be able to comfortably
-     handle those.
+     This routine is only intended for serializing OPFS VFS
+     arguments and (in at least one special case) result values,
+     and the buffer is sized to be able to comfortably handle
+     those.
 
      If passed no arguments then it zeroes out the serialization
      state.
   */
   state.s11n.serialize = function(...args){
+    ++metrics.s11n.serialize.count;
+    const t = performance.now();
     if(args.length){
-      const json = jsonEncoder.encode(JSON.stringify(args));
-      viewSz.setInt32(0, json.byteLength, state.littleEndian);
-      viewJson.set(json);
+      //log("serialize():",args);
+      let i = 0, offset = 1, typeIds = [];
+      viewU8[0] = args.length & 0xff;
+      for(; i < args.length; ++i, ++offset){
+        typeIds.push(getTypeId(args[i]));
+        viewU8[offset] = typeIds[i].id;
+      }
+      for(i = 0; i < args.length; ++i) {
+        const t = typeIds[i];
+        if(t.setter){
+          viewDV[t.setter](offset, args[i], state.littleEndian);
+          offset += t.size;
+        }else{
+          const s = textEncoder.encode(args[i]);
+          viewDV.setInt32(offset, s.byteLength, state.littleEndian);
+          offset += 4;
+          viewU8.set(s, offset);
+          offset += s.byteLength;
+        }
+      }
+      //log("serialize() result:",viewU8.slice(0,offset));
     }else{
-      viewSz.setInt32(0, 0, state.littleEndian);
+      viewU8[0] = 0;
     }
+    metrics.s11n.serialize.time += performance.now() - t;
   };
   return state.s11n;
-};
+}/*initS11n()*/;
 
 const waitLoop = async function f(){
   const opHandlers = Object.create(null);
diff --git a/manifest b/manifest
index a80252bfbe..d5e6c8b22a 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C OPFS\sproxy:\sremove\sone\ssanity-checking-only\slevel\sof\sproxy\sfunction\sto\sshave\soff\sa\sfew\smicroseconds.
-D 2022-09-20T10:47:36.917
+C Speed\sup\sde/serialization\sof\sfunc\sargs\sand\sreturn\svalues\sin\sthe\sOPFS\sVFS\sproxy.
+D 2022-09-20T13:25:39.815
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -484,7 +484,7 @@ F ext/wasm/api/post-js-header.js 0e853b78db83cb1c06b01663549e0e8b4f377f12f5a2d9a
 F ext/wasm/api/sqlite3-api-cleanup.js 8564a6077cdcaea9a9f428a019af8a05887f0131e6a2a1e72a7ff1145fadfe77
 F ext/wasm/api/sqlite3-api-glue.js 366d580c8e5bf7fcf4c6dee6f646c31f5549bd417ea03a59a0acca00e8ecce30
 F ext/wasm/api/sqlite3-api-oo1.js 2d13dddf0d2b4168a9249f124134d37924331e5b55e05dba18b6d661fbeefe48
-F ext/wasm/api/sqlite3-api-opfs.js 10063ff6bc4065a27c81a71f41eb429b53390b5bc885a6305243bf83e3bd94c4
+F ext/wasm/api/sqlite3-api-opfs.js ce75aba0cbfb600cf839362012d17b7b2984aeac5189586c9a5a8f37a573a929
 F ext/wasm/api/sqlite3-api-prologue.js 0d2639387b94c30f492d4aea6e44fb7b16720808678464559458fd2ae3759655
 F ext/wasm/api/sqlite3-api-worker1.js ee4cf149cbacb63d06b536674f822aa5088b7e022cdffc69f1f36cebe2f9fea0
 F ext/wasm/api/sqlite3-wasi.h 25356084cfe0d40458a902afb465df8c21fc4152c1d0a59b563a3fba59a068f9
@@ -519,7 +519,7 @@ F ext/wasm/speedtest1.html 512addeb3c27c94901178b7bcbde83a6f95c093f9ebe16a2959a0
 F ext/wasm/split-speedtest1-script.sh a3e271938d4d14ee49105eb05567c6a69ba4c1f1293583ad5af0cd3a3779e205 x
 F ext/wasm/sql/000-mandelbrot.sql 775337a4b80938ac8146aedf88808282f04d02d983d82675bd63d9c2d97a15f0
 F ext/wasm/sql/001-sudoku.sql 35b7cb7239ba5d5f193bc05ec379bcf66891bce6f2a5b3879f2f78d0917299b5
-F ext/wasm/sqlite3-opfs-async-proxy.js e3c5e1b6416e9c08c713c43fa98319b06fac622ecb813f294b047072b089fba6
+F ext/wasm/sqlite3-opfs-async-proxy.js 9305d92f32d02983c4528b9c801096cfd8295ca7d24e357d90de9bbcb201d035
 F ext/wasm/sqlite3-worker1-promiser.js 4fd0465688a28a75f1d4ee4406540ba494f49844e3cad0670d0437a001943365
 F ext/wasm/sqlite3-worker1.js 0c1e7626304543969c3846573e080c082bf43bcaa47e87d416458af84f340a9e
 F ext/wasm/test-opfs-vfs.html eb69dda21eb414b8f5e3f7c1cc0f774103cc9c0f87b2d28a33419e778abfbab5
@@ -2026,8 +2026,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 88de20712bbe3e11ea74af95edc34e9ab9f346f9aa0a30931e5a9e1f96ce57b0
-R e087e3859232a8d2cb7d73aa59ed1981
+P b534831f3efb8910a17e29956e3e87cc80055ea66e15dbef992b6a556ff042f8
+R 28e069ac7c71e059841784989b21e62c
 U stephan
-Z c97570003be4379736d19c807db44fd0
+Z 483126717a4194dd1997ada5cd19f259
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 3e977d7987..44047c5b0f 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-b534831f3efb8910a17e29956e3e87cc80055ea66e15dbef992b6a556ff042f8
\ No newline at end of file
+5bf235bbe035e4ace7a54851e190742528af6b4266328a1b8bbb9fb3dd7f2118
\ No newline at end of file