I am attempting to use the Redis TYPE command inside a Lua script (executed via EVAL)
local key_type = redis.call("TYPE", key)
According to the Redis documentation, this should return a string of "none", "zset" etc.
However the type of the returned value is a lua table. Comparing the value to a string always returns false.
I've managed to get around the problem by changing the call to
local key_type = redis.call("TYPE", key)["ok"]
This value is indeed a string and does work in string comparison commands. I am worried that this is a bug in my particular version of Redis and it will break in future versions when I upgrade.
Does anyone know if this is expected behaviour, or a bug?
The TYPE command returns a status reply (a.k.a simple string), e.g "+list\r\n".
On Redis scripting side, call is implemented by luaRedisCallCommand which performs the real Redis command behind the scenes.
Once successfully executed, this function converts the command result with redisProtocolToLuaType.
When a status reply is encountered, this function creates a Lua table with "ok" as key, and the status reply as value (see redisProtocolToLuaType_Status). So:
there is no bug,
this is why redis.call("TYPE", key) is a table (and thus you need to get the value for the "ok" key as you did, to get key's type as a string).
Note: when you directly return the table, Redis takes care to get the value associated to the "ok" key, and returns it as a status reply, e.g:
> EVAL 'return redis.call("TYPE", "foo")'
set
See this code section for more details.
Related
I am just starting with language-ext, trying to use it in my Azure Function.
In this function, I first parse/validate the POSTed data from the HTTP request using some validator.
This validator returns an Either<ValidationErrors, RequestModel>.
Then I would like to chain onto the either result a service call that should use the request model to grab some data from an API an return an Option.
At the end of the chain I would then like to return an IActionResult BadRequest if there were ValidationErrors in the first step, or otherwise perform a Match on the result of the service call Option to either return a NotFoundResult or ObjectResult.
The issue I run into is that if I want to chain my service call (using Bind, or BiBind) after the Either<ValidationErrors, GetRequestModel>, then the signature of my service method must be some Either<ValidationErrors, ...>, which is incorrect, since my service method has nothing to do with ValidationErrors. It should just return an Option.
So I guess my question is how can preserve any ValidationErrors until the end of the chain, and be able to chain my service call with a Option signature onto an Either?
You have to decide what the result of your chained expression is.
Option:
var maybeResult = from validated in GetValidationResult(...).ToOption()
from apiResult in ApiCall(...)
select apiResult;
Either:
var resultOrError = from validated in GetValidationResult(...)
from apiResult in ApiCall(...).ToEither(*LEFT*)
select apiResult;
You have to replace *LEFT* by some error value or error generating function returning same type like left type of GetValidationResult.
Replace above pseudo code with your own code and look at the return types of the functions used above to see what's going on.
The reason why you need a common left type is that the bind operation can return some left (error) of first (GetValidationResult) or second (ApiCall) function call -- or right of your last (ApiCall) function if your reach successful end of your chain.
Recommendation: If you mix different left (error) return types you might want to use some thing like LanguageExt's built-in Error type or maybe just a plain string (or Exception).
Either with string as error type:
var resultOrError = from validated in GetValidationResult(...).MapLeft(Prelude.toString)
from apiResult in ApiCall(...).ToEither("api call failed")
select apiResult;
Additional note: I use LINQ style here, you can use method style:
var resultOrError = GetValidationResult(...)
.MapLeft(Prelude.toString)
.Bind(validated => ApiCall(...)
.ToEither("api call failed"));
I tried mongo replica sets for the first time.
I am using ubuntu on ec2 and I booted up three instances.
I used the private IP address of each of the instances. I picked on as the primary and below is the code.
mongo --host Private IP Address
rs.initiate()
rs.add(“Private IP Address”)
rs.addArb(“Private IP Address”)
All at this point is fine. When I go to the http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com:28017/_replSet site I see that I have a primary, seconday, and arbitor.
Ok, now for a test.
On the primary create a database in this is the code:
use tt
db.tt.save( { a : 123 } )
on the secondary, I then do this and get the below error:
db.tt.find()
error: { "$err" : "not master and slaveOk=false", "code" : 13435 }
I am very new to mongodb and replicates but I thought that if I do something in one, it goes to the other. So, if I add a record in one, what do I have to do to replicate across machines?
You have to set "secondary okay" mode to let the mongo shell know that you're allowing reads from a secondary. This is to protect you and your applications from performing eventually consistent reads by accident. You can do this in the shell with:
rs.secondaryOk()
After that you can query normally from secondaries.
A note about "eventual consistency": under normal circumstances, replica set secondaries have all the same data as primaries within a second or less. Under very high load, data that you've written to the primary may take a while to replicate to the secondaries. This is known as "replica lag", and reading from a lagging secondary is known as an "eventually consistent" read, because, while the newly written data will show up at some point (barring network failures, etc), it may not be immediately available.
Edit: You only need to set secondaryOk when querying from secondaries, and only once per session.
To avoid typing rs.slaveOk() every time, do this:
Create a file named replStart.js, containing one line: rs.slaveOk()
Then include --shell replStart.js when you launch the Mongo shell. Of course, if you're connecting locally to a single instance, this doesn't save any typing.
in mongodb2.0
you should type
rs.slaveOk()
in secondary mongod node
THIS IS JUST A NOTE FOR ANYONE DEALING WITH THIS PROBLEM USING THE RUBY DRIVER
I had this same problem when using the Ruby Gem.
To set slaveOk in Ruby, you just pass it as an argument when you create the client like this:
mongo_client = MongoClient.new("localhost", 27017, { slave_ok: true })
https://github.com/mongodb/mongo-ruby-driver/wiki/Tutorial#making-a-connection
mongo_client = MongoClient.new # (optional host/port args)
Notice that 'args' is the third optional argument.
WARNING: slaveOk() is deprecated and may be removed in the next major release. Please use secondaryOk() instead. rs.secondaryOk()
I got here searching for the same error, but from Node.js native driver. The answer for me was combination of answers by campeterson and Prabhat.
The issue is that readPreference setting defaults to primary, which then somehow leads to the confusing slaveOk error. My problem is that I just wan to read from my replica set from any node. I don't even connect to it as to replicaset. I just connect to any node to read from it.
Setting readPreference to primaryPreferred (or better to the ReadPreference.PRIMARY_PREFERRED constant) solved it for me. Just pass it as an option to MongoClient.connect() or to client.db() or to any find(), aggregate() or other function.
https://docs.mongodb.com/v3.0/reference/read-preference/#primaryPreferred
http://mongodb.github.io/node-mongodb-native/3.6/api/Collection.html (search readPreference)
const { MongoClient, ReadPreference } = require('mongodb');
const client = await MongoClient.connect(MONGODB_CONNECTIONSTRING, { readPreference: ReadPreference.PRIMARY_PREFERRED });
slaveOk does not work anymore. One needs to use readPreference https://docs.mongodb.com/v3.0/reference/read-preference/#primaryPreferred
e.g.
const client = new MongoClient(mongoURL + "?readPreference=primaryPreferred", { useUnifiedTopology: true, useNewUrlParser: true });
I am just adding this answer for an awkward situation from DB provider.
what happened in our case is the primary and secondary db shifted reversely (primary to secondary and vice versa) and we are getting the same error.
so please check in the configuration settings for database status which may help you.
Adding readPreference as PRIMARY
const { MongoClient, ReadPreference } = require('mongodb');
const client = new MongoClient(url, { readPreference: ReadPreference.PRIMARY_PREFERRED});
client.connect();
Let's imagine that I have created the stored procedure in SAP HANA database and would like to have optional out parameter with text type, like error details. As I have read to achieve this I should use some default value thus I have done like this:
PROCEDURE "myProcedure"
(
IN inSomeParameter BIGINT,
OUT outResult INTEGER, -- output, result of the operation
OUT outErrorDetail NVARCHAR(32) default ''
)
Unfortunately build failed with the following error:
OUT and IN OUT parameters may not have default expressions
So, I decided to try with null, but it failed the same way. Later I changed the type to integer just to try and it failed exactly same way again.
In the same time this works:
PROCEDURE "myProcedure"
(
IN inSomeParameter BIGINT,
OUT outResult INTEGER, -- output, result of the operation
OUT outErrorDetail TABLE(errorDetails NVARCHAR(32)) default empty
)
but it feels like a huge overkill - to make a table to return only one text value.
Do you have any suggestion how to add optional output parameter?
SQL Script in its current state doesn’t allow for optional OUT parameters.
Why don’t you just set the OUT parameter default value in the procedure body right before the code?
This adds boilerplate code, but you could also use it to convey explicit success messages.
Hi I am using gRPC Ruby plugin to communicate to a service. The proto definition contains(proto3):
uint32 id = 1;
But, when I assign nil to id, it throws an error - expected number for integral field. But for strings, nil values work fine. How do I allow nil values for integral / float fields?
The default values for strings in proto3 is empty -
https://github.com/google/protobuf/issues/359
Hence it can receive the nil value without returning an error, Integers on the other hand have default values set to 0. Try passing 0 in case you do not want to pass any value.
Suggestion: - In case you do not wish to pass any tuples for a message written in proto3 you can leave the message blank which is a very valid way to define a message.
For Instance:-
syntax="proto3"
service Foo{
rpc Index(Empty) Returns(Nothing){}
}
message Empty{}
message Nothing{}
I am using Jedis. I need a Lua script to scan for a pattern with a specified limit. I don't know how to pass the parameters inside Lua script.
Sample Code:
String script="return {redis.call('SCAN',KEYS[1],'COUNT',KEYS[2],'MATCH',KEYS[3]}";
List<String> response = (List<String>)jedis.eval(script,cursor,COUNT,pattern);
How do I pass these parameters to the script?
Your code has several points to fix.
In scan command, 'match' parameter should be placed prior to 'count'.
You should only use KEYS when it is a place for Redis key. Other things should be represented to ARGV.
You forgot to specify key count while calling Jedis.eval().
So, fixed version of your code is,
String script="return {redis.call('SCAN',ARGV[1],'MATCH',ARGV[2],'COUNT',ARGV[3])}";
List<String> response = (List<String>)jedis.eval(script, 0, cursor, pattern, COUNT);
But I agree Itamar to use Jedis.scan() instead.
Hope this helps.