like this then?

Author: brontolosone

lib/model/query/blobs.js

@@ -31,13 +31,14 @@ const getById = (blobId) => ({ maybeOne }) =>
   maybeOne(sql`select * from blobs where id=${blobId}`)
     .then(map(construct(Blob)));
 
-const s3CountByStatus = (status) => ({ oneFirst, run }) => {
-  // Note: This takes out rowlocks on all rows in `blobs`, so
-  // if this is run in a transaction, then those locks aren't
-  // released until the end of the transaction.
-  // Hence the savepoints and rollbacks.
-  // But that brings another potential issue: trying to use a
-  // savepoint outside a transaction is an error.
+const s3CountByStatus = (status) => (db) => {
+  // Note:
+  // To count locked rows, this counts how many rows are left to be locked,
+  // and subtracts that from a total rowcount. Locking rows needs to happen
+  // in a transaction (or one simulated through savepoints) so that the rows
+  // we locked here for just the counting purpose will be released as soon
+  // as we're done counting, rather than at the end of a potential enveloping
+  // transaction.
   const lockCTEs = sql`
     notlockeds AS (
         SELECT 1 FROM blobs FOR NO KEY UPDATE SKIP LOCKED
@@ -51,31 +52,25 @@ const s3CountByStatus = (status) => ({ oneFirst, run }) => {
     )`;
   // in_progress is an implicit status
   if (status === 'in_progress') {
-    return oneFirst(sql`
-      SAVEPOINT peeklocked;
-      WITH ${lockCTEs}
-      SELECT count FROM locked
-    `).then(cnt =>
-      run(
-        sql`ROLLBACK TO SAVEPOINT peeklocked`
-      ).then(() => cnt)
+    return db.transaction(tx =>
+      tx.oneFirst(sql`
+        WITH ${lockCTEs}
+        SELECT count FROM locked
+      `)
     );
   } else if (status === 'pending') {
-    return oneFirst(sql`
-      SAVEPOINT peeklocked;
-      WITH
-        allpending AS (
-          SELECT COUNT(*) FROM blobs WHERE s3_status='pending'
-        ),
-        ${lockCTEs}
-      SELECT allpending.count-locked.count FROM allpending, locked
-    `).then(cnt =>
-      run(
-        sql`ROLLBACK TO SAVEPOINT peeklocked`
-      ).then(() => cnt)
+    return db.transaction(tx =>
+      tx.oneFirst(sql`
+        WITH
+          allpending AS (
+            SELECT COUNT(*) FROM blobs WHERE s3_status='pending'
+          ),
+          ${lockCTEs}
+        SELECT allpending.count-locked.count FROM allpending, locked
+      `)
     );
   } else {
-    return oneFirst(sql`SELECT COUNT(*) FROM blobs WHERE s3_status=${status}`);
+    return db.oneFirst(sql`SELECT COUNT(*) FROM blobs WHERE s3_status=${status}`);
   }
 };
 

lib/util/db.js

@@ -251,6 +251,7 @@ const page = (options) => {
 // it a try and a pull request.
 const queryFuncs = (db, obj) => {
   /* eslint-disable no-param-reassign */
+  obj.transaction = db.transaction;
   obj.run = (s) => db.query(s).then(always(true));
   obj.run.map = () => () => true;