From 443a04fcc471ba6d7de134cd39341df5fad4f3ba Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Tue, 27 Feb 2024 16:21:47 +0000
Subject: [PATCH] Add Head.RebuildSymbolTable

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
---
 tsdb/head.go | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tsdb/head.go b/tsdb/head.go
index b41657ff5..ee5776da2 100644
--- a/tsdb/head.go
+++ b/tsdb/head.go
@@ -2438,3 +2438,35 @@ func (h *Head) ForEachSecondaryHash(fn func(secondaryHash []uint32)) {
 		}
 	}
 }
+
+// WARNING: This code introduces a race - `lset` is accessed without a lock.
+// Go through all the series in h, build a SymbolTable with all names and values,
+// replace each series' Labels with one using that SymbolTable.
+func (h *Head) RebuildSymbolTable() *labels.SymbolTable {
+	st := labels.NewSymbolTable()
+	builder := labels.NewScratchBuilderWithSymbolTable(st, 0)
+	rebuildLabels := func(lbls labels.Labels) labels.Labels {
+		builder.Reset()
+		lbls.Range(func(l labels.Label) {
+			builder.Add(l.Name, l.Value)
+		})
+		return builder.Labels()
+	}
+
+	for i := 0; i < h.series.size; i++ {
+		h.series.locks[i].Lock()
+
+		for _, s := range h.series.hashes[i].unique {
+			s.lset = rebuildLabels(s.lset)
+		}
+
+		for _, all := range h.series.hashes[i].conflicts {
+			for _, s := range all {
+				s.lset = rebuildLabels(s.lset)
+			}
+		}
+
+		h.series.locks[i].Unlock()
+	}
+	return st
+}