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56 lines
2.3 KiB
Plaintext
56 lines
2.3 KiB
Plaintext
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$Id: FAQ.Capacity_Planning.txt,v 1.3 2022/03/22 11:12:25 gilles Exp gilles $
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This documentation is also available online at
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https://imapsync.lamiral.info/FAQ.d/
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https://imapsync.lamiral.info/FAQ.d/FAQ.Capacity_Planning.txt
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======================================================================
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Imapsync tips for Capacity Planning.
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======================================================================
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I plan to go to a distributed architecture for the online service. I'm
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doing some capacity planning. Imapsync takes memory, cpu and bandwidth
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in a relatively deterministic values.
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My current question is: Shall I use
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* N 2GB hosts
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* N/2 4GB hosts
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* N/4 8GB hosts
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Let's do some maths
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The CPU can be an issue. On average, an imapsync run takes 5% of the
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overall cpu time for a Intel i5-2300 with 4 cores. It implies 20
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imapsync runs is ok on the current online host before the cpus become
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the bottleneck. As a rule of thumb, imapsync takes 20% of a cpu core.
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The RAM can be an issue. On average, an imapsync run takes 250 MB. So
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4 imapsync processes per GB is the limit before swapping to disk,
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which is a known phenomenum telling when memory becomes the bottleneck.
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16 GB allows 64 imapsync processes.
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The Bandwidth I/O can be an issue. The "Average bandwidth rate" value
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given by imapsync at the end of a transfer, and also the bandwidth
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rate given during the sync on the ETA line, is the total size of all
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messages copied divided by the time passed. If imapsync is run between
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two foreign imap servers then the total size transferred on the
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network link is twice this value, one time when getting the message
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from host1, rx, and one time sending the message to host2, tx.
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On average, an imapsync runs at 3 Mbps both ways, rx and tx, so 6 Mbps
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in total. So a 100 Mbps symetric link allows 33 imapsync processes
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before the link becomes the bottleneck.
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The best minutes observed so far are a global 187 Mpbs rate (23 MiB/s)
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on a 100 Mbps symetrical link done by 28 imapsync processes in parallel,
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6.7 Mbps per process at that minute. But the best minutes observed for a
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single imapsync process is at 103 Mbps, the rx/tx link limit.
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The harddisk I/O can be an issue. I don't measure it yet because
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imapsync doesn't perform heavy I/0 where it runs. Well, I don't know,
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no measure is no knowledge, just guesses.
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