I.e., the "]"-operator returns 1 if the first string operand collates after the second string operand.​

That's true for String type collations only (e.g. Cache String, Cyrillic2 String, etc). For most other collations defined in Cache (traditionally called Numeric collations) which comply the rule "numbers go first" (e.g. Cache Standard, Cyrillic2) one should use "]]" as "collate after" operator. In common, "]]" seems to be the better choice as it uses current collation rather than String one. This small sample code can demonstrate the difference between "]" and "]]": 

num
 new b,a,i,i0 
 set b("12345678901234567870")="Num20" set b("12345678901234567874")="NotNum20"
 set a=1E30,b(+a)=1,b(+a_"11")=11,b(+a_"111")=111,b(+a_"1a")="3a",a=3E30,b(+a)=3,b(+a_"33")=33,b(+a_"333")=333,b(+a_"1a")="4a"
 set i="",i0="" for  set i=$order(b(i)) quit:i=""  write "(i]]i0)=",i]]i0," (i]i0)=",i]i0," (i>i0)=",i>i0," (i=+i)=",i=+i,?30," " zwrite b(i) set i0=i
 quit

The result for Cache Standard collation is:  

LEARN>d num^ztest
(i]]i0)=1 (i]i0)=1 (i>i0)=1 (i=+i)=1 b(12345678901234567870)="Num20"
(i]]i0)=1 (i]i0)=1 (i>i0)=0 (i=+i)=0 b("12345678901234567874")="NotNum20"
(i]]i0)=1 (i]i0)=0 (i>i0)=1 (i=+i)=1 b(1000000000000000000000000000000)=1
(i]]i0)=1 (i]i0)=1 (i>i0)=1 (i=+i)=1 b(3000000000000000000000000000000)=3
(i]]i0)=1 (i]i0)=0 (i>i0)=1 (i=+i)=0 b("100000000000000000000000000000011")=11
(i]]i0)=1 (i]i0)=1 (i>i0)=1 (i=+i)=0 b("300000000000000000000000000000033")=33
(i]]i0)=1 (i]i0)=0 (i>i0)=1 (i=+i)=0 b("1000000000000000000000000000000111")=111
(i]]i0)=1 (i]i0)=1 (i>i0)=1 (i=+i)=0 b("3000000000000000000000000000000333")=333
(i]]i0)=1 (i]i0)=0 (i>i0)=0 (i=+i)=0 b("10000000000000000000000000000001a")="3a"
(i]]i0)=1 (i]i0)=1 (i>i0)=1 (i=+i)=0 b("30000000000000000000000000000001a")="4a"

While most system administrators may never need or use this function, some employ it for certain kinds of maintenance or other special cases.

Hello Ray, 

I just tried to imagine what kinds of maintenance are better to run with the stopped mirroring:

• Cache version upgrade: just stop Cache - not need to stop mirroring;
• integrity check: maybe, as one may want to have database in stale state to avoid "false positives";
• performing database backup: not sure, as mirrored database(s) would apparently become too late behind the primary one(s) when backup is finished;
• Have I missed something important? Being a consultant and a trainer, I eager to take in account as many special cases as possible...

  Thank you,
  
  Alex

Yet another varaint of 148 characters length (for 8-bit instances only):

ClassMethod am(t) As %String [ ProcedureBlock = 1 ]
{
 s s="",a="!""#123ABCQRSabcqrstЃ‚ѓ‘’“”•" f i=1:1:$l(t){s p=$a(a,$a(t,i)-96),j=p\16 s:$e(s,*)=j s=s_" " s s=s_$s(j:$tr($j("",p#16)," ",j),1:0)} q s
}

Not sure about Debian Jessie, but for Ubuntu you should use SUSE_x86_64 (rather than RHEL_x86_64) tarball.

It seems that George James Software (like some other M houses) followed MSM traditions where all command and function users' extensions names could started with 'ZZ' only.

We at SP.ARM have some command extensions as well, and all of them are named as 'ZZ*'. E.g., ZZU - CHUI based namespace navigator, which was originally written for MSM many years ago (when 'U' meant 'UCI') and ported to Cache among first handy tools we used those days (y2k +/-1).

This old ZZ-rule was rather convenient as it naturally separated users' extensions (ZZ*) from system ones (Z<not Z>*).

Thank you for excellent articles, Murray.

We use slightly different approach for memory planning.

Our app mostly runs as a set of concurrent user sessions, one process per user. It's known that avg memory per process is 10Mb, we multiply it by 3*N_concurrent_users. The 1st multiplier (3) makes a gap for memory spikes. So, the result is a memory we leave for user processes.

We try to leave for Routine Buffer cache as much memory as possible, upto 1Gb.

The Global Buffer memory is usually calculated as a 30% of 3-years-old-database size for given kind of customer. Usually it comes to 24-64Gb global cache for medium to large size hospitals and provides thousands (or dozens of thousands) Rdratio. At whole, we usually get numbers that are close to your 60/40 proportion, while my globuff calculation method is not so presized as yours and I feel that I need a better calculation base for it.

Hi Mark,

May I ask you to clarify a bit.
Am I right thinking that journal transfer is acknowledged only when it runs between failover nodes, so network latency is not a great problem for async communications? Of course, the bigger latency the bigger journal transfer delay, but it would not slow down the primary node operation.
E.g., if we have average 10-20 JrnWrts per second during each busy hour (with spikes up to 300), for right async WAN planning I should take in account that the latency <= 50 ms (1000/20=50) should be sufficient if we can live with DR async node that is usually about several seconds behind the primary?

As I can remind, shadowing allows cascading. Don't you think that cascading can be a good option for deploying of several async nodes at one (long distance) location as well?

Thanks,
Alex
 

Thank you for the article, Mark. I have a couple of questions on your "Option 3: Geographically Dispersed Deployments".

You placed two DR acync nodes at Data Center B. So, the data flow from Primary (at Data Center A) to DR async (at Data Center B) will be doubled. In general, WAN is not too quick, so it may increase latency. More important that mirrored databases at both DR async nodes may have different states (due to different latency), and it would be difficult to decide which of them should be promoted as a new Primary.
And how to catch up the database at the new Secondary, if we can't guarantee that it is in the same state as at the new Primary?

Another useful method for cache.key analyzing is: 

do $system.License.DecodeAuth("<AuthorizationKey>")

which displays the capabilities encoded in the <AuthorizationKey> field of a given cache.key file (should be copy-pasted from the file). Argument-less method:

do $system.License.Decode()

does the same for active license key.

In Cache 2015+ you need not put a new cache.key in MGR directory manually any more, as SMP>Activate New License page has got an option to browse server's file system. After you have chosen the key file, SMP checks it up and copies to MGR automatically. This option simplifies much the searching of right directory, especially for new users.

Just noticed the following "reformatted" code fragment:

if zzz'["" { ... }

Well-well, Ed. The intention of following check up:

if zzzzzzZ'["zzzz" 

was to avoid logging my own variables which names were deliberately started with this nasty prefix. I agree that it's rather naive trick, but it worked.
As to original code, it was taken from the existing code base and complied our internal coding standards; I preferred to publish it "as is", having neither time nor will to re-test it.

Just adding my 2c to "4. Tip For UNIX sites":
All necessary unix/linux packages should be installed before the first invocation of 

Do run^pButtons(<any profile>)

otherwise some commands may be missed in ^pButtons("cmds"). I've recently faced it at the server where sysstat wasn't installed: `sar -d` and `sar -u` commands were absent. If you decide to install it later (`sudo yum install sysstat`in my case), ^pButtons("cmds") would not be automatically updated without little help from you: just kill it before calling the run^pButtons().

This is actual at least for pButtons v.1.15c-1.16c and v.5 (which recently occurred on ftp://ftp.intersys.com/pub/performance/), in Caché 2015.1.2.

Rdratio is a little more interesting — it is the ratio of logical block reads to physical block reads.

Don't you think that zero values of Rdratio is a special case, as David Marcus mentioned?
In mgstat (per second) logs I have at hand I've found them always accompanied with zero values of PhyRds.

Murray, thank you for the series of articles.

A couple of questions I have.

1) Documentation (2015.1) states that Rdratio is a Ratio of physical block reads to logical block reads,
while one can see in mgstat log Rdratio values >> 1 (usually 1000 and more). Don't you think that the definition should be reversed?

2) You wrote that:
If you do see high PhyRds on your system there are a couple of strategies you can consider:
...
- Long running read only reports, batch jobs or data extracts can be run on a separate shadow server or asynchronous mirror to minimise impact on interactive users and to offload system resource use such as CPU and IOPS.

I heard this advice many times, but how to return report results back to primary member? (ECP) mounting of remote database that resides on primary member is prohibited on backup member, and vise versa. Or these restrictions does not apply to asynchronous members (never played with them yet)?
 

Hi Mark,

You are right, in our setup Cache' is able to remove/assign the VIP to whichever node is the primary mirror member. All production traffic goes through ECP, so the mirror's VIP is used to simplify some administrative tasks only (just to recognize primary node quicker).

Virtual router is a standard component of vCloud Director, so called Edge Gateway. It sits between a single external address and internal load balancer implemented as a couple of Linux based VMs, each of which has haproxy for balancing and ucarp for VIP/failover. Load balancer distributes incoming client connections among several ECP application servers (Linux based VMs as well). 

That's how it works, in short. If somebody is interested in more verbose description, I could write more about it.

Regards,
Alex