Sketch out spec text for durability. Fixes #50

index.bs

@@ -957,6 +957,21 @@ a [=/transaction=] with [=transaction/mode=] {{"readonly"}}.
 A <dfn>read/write transaction</dfn>
 is a [=/transaction=] with [=transaction/mode=] {{"readwrite"}}.
 
+A [=/transaction=] has a <dfn>durability</dfn> hint. This is a hint to the user agent of whether to prioritize performance or durability when committing the transaction.
+
+: {{"strict"}}
+:: The user agent may consider that the [=/transaction=] has successfully [=transaction/committed=] only after verifying that all outstanding changes have been successfully written to a persistent storage medium.
+: {{"relaxed"}}
+:: The user agent may consider that the [=/transaction=] has successfully [=transaction/committed=] as soon as all outstanding changes have been written to the operating system, without subsequent verification.
+: {{"default"}}
+:: The user agent should use its default durability behavior for the storage [=/bucket=].
+
+<aside class=note>
+  In a typical implementation, {{"strict"}} is a hint to the user agent to flush any operating system I/O buffers before a {{"complete"}} event is fired. While this provides greater confidence that the changes will be persisted in case of subsequent operating system crash or power loss, flushing buffers can take significant time and consume battery life on portable devices.
+
+  Web applications are encouraged to use {{"relaxed"}} for ephemeral data such as caches or quickly changing records, and {{"strict"}} in cases where reducing the risk of data loss outweighs the impact to performance and power. Implementations are encouraged to weigh the durability hint from applications against the impact to users and devices.
+</aside>
+
 <!-- ============================================================ -->
 ### Transaction Lifecycle ### {#transaction-lifecycle}
 <!-- ============================================================ -->
@@ -2449,7 +2464,8 @@ interface IDBDatabase : EventTarget {
   readonly attribute DOMStringList objectStoreNames;
 
   [NewObject] IDBTransaction transaction((DOMString or sequence<DOMString>) storeNames,
-                                         optional IDBTransactionMode mode = "readonly");
+                                         optional IDBTransactionMode mode = "readonly",
+                                         optional IDBTransactionOptions options = {});
   void close();
 
   [NewObject] IDBObjectStore createObjectStore(
@@ -2464,6 +2480,12 @@ interface IDBDatabase : EventTarget {
   attribute EventHandler onversionchange;
 };
 
+enum IDBTransactionDurability { "default", "strict", "relaxed" };
+
+dictionary IDBTransactionOptions {
+  IDBTransactionDurability durability = "default";
+};
+
 dictionary IDBObjectStoreParameters {
   (DOMString or sequence<DOMString>)? keyPath = null;
   boolean autoIncrement = false;
@@ -2661,8 +2683,7 @@ instance on which it was called.
 
 <div class=algorithm>
 
-The <dfn method for=IDBDatabase>transaction(|storeNames|,
-|mode|)</dfn> method, when invoked, must run these steps:
+The <dfn method for=IDBDatabase>transaction(|storeNames|, |mode|, |options|)</dfn> method, when invoked, must run these steps:
 
 1. If a running [=/upgrade transaction=] is associated with the [=/connection=],
     [=throw=] an "{{InvalidStateError}}" {{DOMException}}.
@@ -2683,9 +2704,7 @@ The <dfn method for=IDBDatabase>transaction(|storeNames|,
 1. If |mode| is not {{"readonly"}} or {{"readwrite"}},
     [=throw=] a [=TypeError=].
 
-1. Let |transaction| be a newly [=transaction/created=] [=/transaction=] with
-    |connection|, |mode| and the set of [=/object stores=] named in
-    |scope|.
+1. Let |transaction| be a newly [=transaction/created=] [=/transaction=] with |connection|, |mode|, |options|' {{IDBTransactionOptions/durability}} member, and the set of [=/object stores=] named in |scope|.
 
 1. Set |transaction|'s [=transaction/cleanup event loop=] to the
     current [=event loop=].
@@ -4860,6 +4879,8 @@ attribute's getter must run these steps:
 The <dfn attribute for=IDBTransaction>mode</dfn> attribute's getter
 must return **this**'s [=transaction/mode=].
 
+The <dfn attribute for=IDBTransaction>durability</dfn> attribute's getter must return the [=transaction/durability=] of the [=/transaction=].
+
 The <dfn attribute for=IDBTransaction>db</dfn> attribute's getter must
 return **this**'s [=transaction/connection=]'s associated [=/database=].
 
@@ -5198,7 +5219,7 @@ To <dfn>commit a transaction</dfn> with the |transaction| to commit, run these s
     1. If |transaction|'s [=transaction/state=] is no longer [=transaction/committing=],
         then terminate these steps.
 
-    1. Attempt to write any outstanding changes made by |transaction| to the [=database=].
+    1. Attempt to write any outstanding changes made by |transaction| to the [=database=], considering |transaction|'s [=transaction/durability=] hint.
 
     1. If an error occurs while writing the changes to the [=database=],
         then run [=abort a transaction=] with |transaction| and an
@@ -6814,6 +6835,7 @@ For the revision history of the second edition, see [that document's Revision Hi
 * Added {{IDBCursor/request}} attribute. ([Issue #255](https://github.com/w3c/IndexedDB/issues/255))
 * Removed handling for nonstandard `lastModifiedDate` property of {{File}} objects. ([Issue #215](https://github.com/w3c/IndexedDB/issues/215))
 * Remove escaping {{IDBKeyRange/includes()}} method. ([Issue #294](https://github.com/w3c/IndexedDB/issues/294))
+* Added {{IDBTransactionOptions/durability}} option and {{IDBTransaction/durability}} attribute. ([Issue #50](https://github.com/w3c/IndexedDB/issues/50))
 
 <!-- ============================================================ -->
 # Acknowledgements # {#acknowledgements}
@@ -6877,6 +6899,7 @@ Yaron Tausky,
 Bevis Tseng,
 Ben Turner,
 Kyaw Tun,
+Adrienne Walker,
 Hans Wennborg,
 Shawn Wilsher,
 Brett Zamir,