From 818242f4520e4a1477b80c1a69ae5fbb7a854098 Mon Sep 17 00:00:00 2001
From: ccase <caleb@storj.io>
Date: Wed, 22 Jan 2020 11:10:14 -0500
Subject: [PATCH] storage/postgreskv: Reverting back to the venerable PG CAS

This was inadvertently converted to the Cockroach version. This reverts
most of that and keeps the changes since then.

Change-Id: Ia440eeebb01bc89fbfa8ce266668030173061469
---
 storage/postgreskv/client.go | 94 +++++++++++++++++-------------------
 1 file changed, 43 insertions(+), 51 deletions(-)

diff --git a/storage/postgreskv/client.go b/storage/postgreskv/client.go
index 3940c6641..0d700719e 100644
--- a/storage/postgreskv/client.go
+++ b/storage/postgreskv/client.go
@@ -4,7 +4,6 @@
 package postgreskv
 
 import (
-	"bytes"
 	"context"
 	"database/sql"
 
@@ -14,7 +13,6 @@ import (
 
 	"storj.io/storj/private/dbutil"
 	"storj.io/storj/private/dbutil/pgutil"
-	"storj.io/storj/private/dbutil/txutil"
 	"storj.io/storj/private/tagsql"
 	"storj.io/storj/storage"
 	"storj.io/storj/storage/postgreskv/schema"
@@ -201,6 +199,7 @@ func (client *Client) CompareAndSwap(ctx context.Context, key storage.Key, oldVa
 		if err != nil {
 			return Error.Wrap(err)
 		}
+
 		return storage.ErrValueChanged.New("%q", key)
 	}
 
@@ -217,62 +216,55 @@ func (client *Client) CompareAndSwap(ctx context.Context, key storage.Key, oldVa
 		if err == sql.ErrNoRows {
 			return storage.ErrValueChanged.New("%q", key)
 		}
+
 		return Error.Wrap(err)
 	}
 
-	return txutil.WithTx(ctx, client.db, nil, func(_ context.Context, txn tagsql.Tx) error {
-		q := "SELECT metadata FROM pathdata WHERE fullpath = $1::BYTEA;"
-		row := txn.QueryRowContext(ctx, q, []byte(key))
-
-		var metadata []byte
-		err = row.Scan(&metadata)
-		if err == sql.ErrNoRows {
-			// Row not found for this fullpath.
-			// Potentially because another concurrent transaction changed the row.
-			return storage.ErrKeyNotFound.New("%q", key)
-		}
-		if err != nil {
-			return Error.Wrap(err)
-		}
-
-		if equal := bytes.Compare(metadata, oldValue); equal != 0 {
-			// If the row is found but the metadata has been already changed
-			// we can't continue to delete it.
-			return storage.ErrValueChanged.New("%q", key)
-		}
-
-		var res sql.Result
-		if newValue == nil {
-			q = `
-		DELETE FROM pathdata
-			WHERE pathdata.fullpath = $1::BYTEA
-				AND pathdata.metadata = $2::BYTEA
+	var row *sql.Row
+	if newValue == nil {
+		q := `
+		WITH matching_key AS (
+			SELECT * FROM pathdata WHERE fullpath = $1::BYTEA
+		), updated AS (
+			DELETE FROM pathdata
+				USING matching_key mk
+				WHERE pathdata.metadata = $2::BYTEA
+					AND pathdata.fullpath = mk.fullpath
+				RETURNING 1
+		)
+		SELECT EXISTS(SELECT 1 FROM matching_key) AS key_present, EXISTS(SELECT 1 FROM updated) AS value_updated
 		`
-
-			res, err = txn.ExecContext(ctx, q, []byte(key), []byte(oldValue))
-		} else {
-			q = `
-		UPDATE pathdata
-			SET metadata = $3::BYTEA
-			WHERE pathdata.fullpath = $1::BYTEA
-				AND pathdata.metadata = $2::BYTEA
+		row = client.db.QueryRow(ctx, q, []byte(key), []byte(oldValue))
+	} else {
+		q := `
+		WITH matching_key AS (
+			SELECT * FROM pathdata WHERE fullpath = $1::BYTEA
+		), updated AS (
+			UPDATE pathdata
+				SET metadata = $3::BYTEA
+				FROM matching_key mk
+				WHERE pathdata.metadata = $2::BYTEA
+					AND pathdata.fullpath = mk.fullpath
+				RETURNING 1
+		)
+		SELECT EXISTS(SELECT 1 FROM matching_key) AS key_present, EXISTS(SELECT 1 FROM updated) AS value_updated;
 		`
-			res, err = txn.ExecContext(ctx, q, []byte(key), []byte(oldValue), []byte(newValue))
-		}
+		row = client.db.QueryRow(ctx, q, []byte(key), []byte(oldValue), []byte(newValue))
+	}
 
-		if err != nil {
-			return Error.Wrap(err)
-		}
+	var keyPresent, valueUpdated bool
+	err = row.Scan(&keyPresent, &valueUpdated)
+	if err != nil {
+		return Error.Wrap(err)
+	}
 
-		affected, err := res.RowsAffected()
-		if err != nil {
-			return Error.Wrap(err)
-		}
+	if !keyPresent {
+		return storage.ErrKeyNotFound.New("%q", key)
+	}
 
-		if affected != 1 {
-			return storage.ErrValueChanged.New("%q", key)
-		}
+	if !valueUpdated {
+		return storage.ErrValueChanged.New("%q", key)
+	}
 
-		return nil
-	})
+	return nil
 }