From bbdc20f8cafc63e768f248213eafe65f163cb6e5 Mon Sep 17 00:00:00 2001
From: Patrick Molgaard <patrick@loyaltylion.com>
Date: Tue, 31 May 2022 16:56:42 +0100
Subject: [PATCH] perf: partially lift matching from regexp to js (#9032)

Digging further into #3857.

See also #8955, #8956.

As [previously
discussed](https://github.com/typeorm/typeorm/issues/3857#issuecomment-699505893),
the query builder currently suffers from poor performance in two ways:
quadratic numbers of operations with respect to total table/column
counts, and poor constant factor performance (regexps can be expensive
to build/run!)

The constant-factor performance is the more tractable problem: no longer
quadratically looping would be a chunky rewrite of the query builder,
but we can locally refactor to be a bunch cheaper in terms of regexp
operations.

This change cuts the benchmark time here in ~half (yay!).

We achieve this by simplifying the overall replacement regexp (we don't
need our column names in there, since we already have a plain object
where they're the keys to match against) so compilation of that is much
cheaper, plus skipping the need to `escapeRegExp` every column as a
result.
---
 src/query-builder/QueryBuilder.ts             | 40 +++++++++----------
 .../multiple-joins-querybuilder.ts            | 10 ++---
 2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/src/query-builder/QueryBuilder.ts b/src/query-builder/QueryBuilder.ts
index 88da9bebef..83f76e0260 100644
--- a/src/query-builder/QueryBuilder.ts
+++ b/src/query-builder/QueryBuilder.ts
@@ -756,27 +756,27 @@ export abstract class QueryBuilder<Entity> {
                 replacements[column.propertyPath] = column.databaseName
             }
 
-            const replacementKeys = Object.keys(replacements)
-
-            if (replacementKeys.length) {
-                statement = statement.replace(
-                    new RegExp(
-                        // Avoid a lookbehind here since it's not well supported
-                        `([ =\(]|^.{0})` +
-                            `${escapeRegExp(
-                                replaceAliasNamePrefix,
-                            )}(${replacementKeys
-                                .map(escapeRegExp)
-                                .join("|")})` +
-                            `(?=[ =\)\,]|.{0}$)`,
-                        "gm",
-                    ),
-                    (_, pre, p) =>
-                        `${pre}${replacementAliasNamePrefix}${this.escape(
+            statement = statement.replace(
+                new RegExp(
+                    // Avoid a lookbehind here since it's not well supported
+                    `([ =\(]|^.{0})` + // any of ' =(' or start of line
+                        // followed by our prefix, e.g. 'tablename.' or ''
+                        `${escapeRegExp(
+                            replaceAliasNamePrefix,
+                        )}([^ =\(\)\,]+)` + // a possible property name: sequence of anything but ' =(),'
+                        // terminated by ' =),' or end of line
+                        `(?=[ =\)\,]|.{0}$)`,
+                    "gm",
+                ),
+                (match, pre, p) => {
+                    if (replacements[p]) {
+                        return `${pre}${replacementAliasNamePrefix}${this.escape(
                             replacements[p],
-                        )}`,
-                )
-            }
+                        )}`
+                    }
+                    return match
+                },
+            )
         }
 
         return statement
diff --git a/test/benchmark/multiple-joins-querybuilder/multiple-joins-querybuilder.ts b/test/benchmark/multiple-joins-querybuilder/multiple-joins-querybuilder.ts
index 7c26b6ee0a..0841f23610 100644
--- a/test/benchmark/multiple-joins-querybuilder/multiple-joins-querybuilder.ts
+++ b/test/benchmark/multiple-joins-querybuilder/multiple-joins-querybuilder.ts
@@ -47,11 +47,11 @@ describe("benchmark > QueryBuilder > wide join", () => {
 
         /**
          * On a M1 macbook air, 5 runs:
-         * 3501ms
-         * 3574ms
-         * 3575ms
-         * 3563ms
-         * 3567ms
+         * 1861ms
+         * 1850ms
+         * 1859ms
+         * 1859ms
+         * 1884ms
          */
     })
 })