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From: Junio C Hamano <>
To: Jeff Hostetler <>
Cc: "Neeraj K. Singh via GitGitGadget" <>,, "Neeraj K. Singh" <>,
	Neeraj Singh <>
Subject: Re: [PATCH] read-cache: make the index write buffer size 128K
Date: Fri, 19 Feb 2021 19:28:00 -0800	[thread overview]
Message-ID: <xmqqv9ana05b.fsf@gitster.g> (raw)
In-Reply-To: <> (Jeff Hostetler's message of "Fri, 19 Feb 2021 14:12:42 -0500")

Jeff Hostetler <> writes:

> On 2/17/21 9:48 PM, Neeraj K. Singh via GitGitGadget wrote:
>> From: Neeraj Singh <>
>> Writing an index 8K at a time invokes the OS filesystem and caching
>> code
>> very frequently, introducing noticeable overhead while writing large
>> indexes. When experimenting with different write buffer sizes on Windows
>> writing the Windows OS repo index (260MB), most of the benefit came by
>> bumping the index write buffer size to 64K. I picked 128K to ensure that
>> we're past the knee of the curve.
>> With this change, the time under do_write_index for an index with 3M
>> files goes from ~1.02s to ~0.72s.
> [...]
>>   -#define WRITE_BUFFER_SIZE 8192
>> +#define WRITE_BUFFER_SIZE (128 * 1024)
>>   static unsigned char write_buffer[WRITE_BUFFER_SIZE];
>>   static unsigned long write_buffer_len;
> [...]
> Very nice.

I wonder if we gain more by going say 4M buffer size or even larger?

Is this something we can make the system auto-tune itself?  This is
not about reading but writing, so we already have enough information
to estimate how much we would need to write out.


  reply	other threads:[~2021-02-20  3:29 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-18  2:48 [PATCH] read-cache: make the index write buffer size 128K Neeraj K. Singh via GitGitGadget
2021-02-19 19:12 ` Jeff Hostetler
2021-02-20  3:28   ` Junio C Hamano [this message]
2021-02-20  7:56     ` Neeraj Singh
2021-02-21 12:51       ` Junio C Hamano
2021-02-24 20:56         ` Neeraj Singh
2021-02-25  5:41           ` Junio C Hamano
2021-02-25  6:58             ` Chris Torek
2021-02-25  7:16               ` Junio C Hamano
2021-02-25  7:36                 ` Neeraj Singh
2021-02-25  7:57                   ` Chris Torek

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