From 2f9371516df8fb00724e8b76dc5753a3a51136b1 Mon Sep 17 00:00:00 2001
From: Andrew Kane <andrew@ankane.org>
Date: Mon, 15 Jan 2024 19:17:50 -0800
Subject: [PATCH] Leave space for other objects in shared memory

---
 src/hnswbuild.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/hnswbuild.c b/src/hnswbuild.c
index b92bdc9..b683b24 100644
--- a/src/hnswbuild.c
+++ b/src/hnswbuild.c
@@ -931,6 +931,7 @@ HnswBeginParallel(HnswBuildState * buildstate, bool isconcurrent, int request)
 	Snapshot	snapshot;
 	Size		esthnswshared;
 	Size		esthnswarea;
+	Size		estother;
 	HnswShared *hnswshared;
 	char	   *hnswarea;
 	HnswLeader *hnswleader = (HnswLeader *) palloc0(sizeof(HnswLeader));
@@ -961,7 +962,15 @@ HnswBeginParallel(HnswBuildState * buildstate, bool isconcurrent, int request)
 	/* Estimate size of workspaces */
 	esthnswshared = ParallelEstimateShared(buildstate->heap, snapshot);
 	shm_toc_estimate_chunk(&pcxt->estimator, esthnswshared);
+
+	/* Leave space for other objects in shared memory */
+	/* Docker has a default limit of 64 MB for shm_size */
+	/* which happens to be the default value of maintenance_work_mem */
 	esthnswarea = maintenance_work_mem * 1024L;
+	estother = 2 * 1024 * 1024;
+	if (esthnswarea > estother)
+		esthnswarea -= estother;
+
 	shm_toc_estimate_chunk(&pcxt->estimator, esthnswarea);
 	shm_toc_estimate_keys(&pcxt->estimator, 2);