From 7aff8299be45b67e8d80804a526e4455dd421e3e Mon Sep 17 00:00:00 2001 From: "Tim Slavin (MongoDB)" Date: Mon, 8 Sep 2014 09:39:17 -0400 Subject: [PATCH] DOCS-3951: Document 1MB RAM for thread connections --- source/faq/diagnostics.txt | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/source/faq/diagnostics.txt b/source/faq/diagnostics.txt index f62e5f12699..0ba85e57f5d 100644 --- a/source/faq/diagnostics.txt +++ b/source/faq/diagnostics.txt @@ -87,7 +87,7 @@ Windows systems. What tools are available for monitoring MongoDB? ------------------------------------------------ -The `MongoDB Management Services `_ includes +The `MongoDB Management Services ` includes monitoring. MMS Monitoring is a free, hosted services for monitoring MongoDB deployments. A full list of third-party tools is available as part of the :doc:`/administration/monitoring/` documentation. Also @@ -200,6 +200,8 @@ limited to: - The number or rate of page faults and other MMS gauges to detect when you need more RAM +- Each database connection thread will need up to 1 MB of RAM. + MongoDB defers to the operating system when loading data into memory from disk. It simply :ref:`memory maps ` all its data files and relies on the operating system to cache data. The OS @@ -211,7 +213,8 @@ your particular usage. To calculate how much RAM you need, you must calculate your working set size, or the portion of your data that clients use most often. This depends on your access patterns, what indexes you have, and the size of -your documents. +your documents. Because MongoDB uses a thread per connection model, each +database connection also will need up to 1MB of RAM, whether active or idle. If page faults are infrequent, your working set fits in RAM. If fault rates rise higher than that, you risk