Carlo Stonebanks wrote:
<<effective_cache_size should be set to how much memory is leftover
for disk caching after taking into account what's used by the
operating system, dedicated PostgreSQL memory, and other applications.
If it's set too low, indexes may not be used for executing queries the
way you'd expect. Setting effective_cache_size to 1/2 of total memory
would be a normal conservative setting. You might find a better
estimate by looking at your operating system's statistics. On
UNIX-like systems, add the free+cached numbers from free or top. On
Windows see the "System Cache" in the Windows Task Manager's
Performance tab.
Are these values to look at BEFORE starting PG? If so, how do I relate
the values returned to setting the effective_cache_size values?
After starting the database. You can set effective_cache_size to a size
in megabytes, so basically you'd look at the amount of free cache, maybe
round down a bit, and set effective_cache_size to exactly that. It's
not super important to get the number right. The point is that the
default is going to be a tiny number way smaller than the RAM in your
system, and even getting it within a factor of 2 or 3 of reality will
radically change some types of query plans.
PS Loved your 1995 era pages. Being a musician, it was great to read
your recommendations on how to buy these things called "CD's". I
Googled the term, and they appear to be some ancient precursor to MP3s
which people actually PAID for. What kind of stone were they engraved
on? ;-D
They're plastic, just like the iPod, iPhone, iToilet, or whatever other
white plastic Apple products people listen to music during this new
era. Since both my CD collection and the stereo I listen to them on are
each individually worth more than my car, it's really tough to sell me
on all the terrible sounding MP3s I hear nowadays. I'm the guy who can
tell you how the LP, regular CD, gold CD, and SACD/DVD-A for albums I
like all compare, so dropping below CD quality is right out. If you
ever find yourself going "hey, I wish I had six different versions of
'Dark Side of the Moon' around so I could compare the subtle differences
in the mastering and mix on each of them", I'm your guy.
--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg@xxxxxxxxxxxxxxx www.2ndQuadrant.com
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