I am new to Go, and trying to get the estimate size of a Thrift generated object in Go, the object has multiple level, and in the case of an member variable is an collection of pointers, I want to get the total size of pointer and the data that been pointed to. The sizeOf function won't work in this case, as it will only count the space taken by the pointer, not the actual space. What's the best way to get a good estimate of the size of the object? Ideally, I would like to breakdown the size into different fields and subfields
Here is how an example object looks like in Go
type Microshard struct {
Header *Header `thrift:"header,1,required"`
ValidatorStats []*ValidatorStat `thrift:"validatorStats,2,required"`
DataMap1 map[int64][]byte `thrift:"dataMap1,3,required"`
DataMap2 map[int64][]byte `thrift:"dataMap2,4,required"`
DataMap3 map[int64][]int64 `thrift:"dataMap3,5,required"`
DebugInfoMap map[string][]byte `thrift:"debugInfoMap,6,required"`
Index *IndexData `thrift:"index,7"`
}
Related
Im new in Go-EVM, and some time ago I got a source code to get transaction tracking. But some functions in the source codes have been updated and changed, here are some questions I wanna ask:
The first one is: How to get *snapshot.Tree?
stateDB, err := state.New(block.Root(), state.NewDatabase(db))
Now this statements need three parameter and the lost parameter's type is *sanpshot.Tree. It is a struct, here is the link to its source code, in line 164.
The second one is: What are AsseccList and GasTipFee?
message := types.NewMessage(from, tx.To(), 0, tx.Value(), tx.Gas(), from Address, to Address, nonce, amount, gasLimit, tx.GasPrice(), GasTopfee, GasTipFee, tx.Data(), accesslist AccessList, false)
AccessList is also a struct. You can see its struct from here. What should I input into AccessList and GasTipFee?
Really appreciate it if you can help me solve these questions.
In your case you do not need to pass a tree snapshot if you do not have one. The purpose of the tree snapshot is to, if the snapshot matches with the given root of the block's trie, run what they call a pre-fetcher routine, that is in charge of preloading nodes in memory so that when the state reaches the commit phase, it is more performant because it already has most of the required nodes in memory. So in your case, you should be perfectly fine passing nil to that constructor.
As for the AccessList and GasTipFee parameters:
AccessList is an EIP-2930 access list. It's once again something optional that transactions can provide to specify the addresses and storage keys that they need access to. Once again you can provide a nil slice.
What you have called GasTipFee is called GasTipCap on master and is basically the limit value of a gas tip, as far as I understand. You can find more information on gas fees in the official documentation.
I am working on a search filter atm where people can specify things like (example) size, color, fabric and so on.
Obviously I have models for each i.e. size, color and fabric. But since this "search" should return every result i.e. size + color + fabric and not just one of the three I would need to make a new struct which contains all the (size, color and fabric) to be able to consume the result that Gorm would return.
Since we have a LOT of filters, this could get very messy. Does anyone know if there is a better way to do it? or what would be a best practice to do this?
type Result struct {
ID int
Name string
Age int
}
var result Result
db.Raw("SELECT id, name, age FROM users WHERE name = ?", 3).Scan(&result)
The above example illustrates how I think it should be done, but as you can expect with the amount of data I need to return this struct would become huge.
The results are quite large in terms of data. I mean what I would want in return in the final version for example (this is about sales):
What products were bought, the amount, color and size. Payment data i.e. price, tax, payment method. Customer information, et cetera.
So in total there is a lot of information to store.
All this information should be returned as a JSON format so we can call it through an API call.
Each call should give back 100 up to 15.000 results, to give you an idea of the side of the data.
Hope someone can explain a bit about a best practice method and -or how I should solve this problem as I am unsure on how to code this effectively.
I have a slice of struct. I am trying to copy this slice to new variable since my original slice changes a lot
model for sheet
type Timesheet struct {
ID *int64 `json:"id"`
TimestampStart *time.Time `json:"timestampStart"`
TimestampEnd *time.Time `json:"timestampEnd"`
}
SheetArrayCopy := make([]models.Sheet, len(sheetList))
copy(SheetArrayCopy, SheetList)
//several steps which goes through SheetList and changes the value of sheetList
However when I change the value in sheetList, the values of SheetArrayCopy also changes.
From your question and #Masklinn example link. I can see that you set value by using *pointer (address that pointer points to) which means set the value of that address to the new value.
There is nothing to do with
copy
Which is doing exactly which it means. And in this case, it clone the value of the fields' pointers which is pointing to the address of the fields' values.
The problem is the way you use and set value of the pointers.
There are 3 ways, to avoid the problem you mentioned about.
Write your custom clone slice which init new structs and clone only the values from original slice to the new.
Still using the clone, but when you set the value of the fields, set the fields' pointers to the new address. Others slices' items pointers still point to the old value.
Don't use pointer if you don't have any special reason.
You can ref to my code which is the demonstration of my answer.
https://play.golang.org/p/-pIgEDEr-hI
Link about the pointer which points out directly about how to use pointer.
https://tour.golang.org/moretypes/1
maybe you can covert that back to json and unmarsal that json to its new destination.
My goal is to get to the raw driver.Value values as deserialized by a sql driver in its implementation of driver.Rows.Next(). I want to handle the conversion from the values returned by the driver to the needed target types, instead of relying on the automatic conversions built in to Rows.Scan. Note this question does not ask your opinion on whether Rows.Scan "should" be used. I don't want to use it, and I am asking if there is any way to avoid it.
A meaningful answer does not use Rows.Scan at all. The dynamic approach illustrated in Working with Unknown Columns is awful: It invokes all the overhead of Scan and destroys the type information of the source columns, instead shredding the actual driver.Values into SqlBytes.
The following hack works, but relies on the internal implementation detail that sql.Rows.Next() populates the internal field lastcols with exactly the unconverted values which I want:
vpRows := reflect.ValueOf(rows) // rows is a *sql.Rows
vRows := reflect.Indirect(vpRows) // now we have the sql.Rows struct
mem := vRows.FieldByName("lastcols") // unexported field lastcols
unsafeLastCols := unsafe.Pointer(mem.UnsafeAddr()) // Evil
plastCols := (*[]driver.Value)(unsafeLastCols) // But effective
for rows.Next() {
rowVals := *plastCols
fmt.Println(rowVals)
}
The normal solution is to implement your own sql.Scanner. But this does use rows.Scan, so it violates your mysterious requirement not to use rows.Scan.
If you truly must avoid rows.Scan, you'll need to write your own driver implementation (possibly wrapping an existing driver) which provides access to the driver.Value values without rows.Scan.
I have a HashMap<u32, Sender>. Sender is a open connection object and the key is a user id. Each user can connect from multiple devices. I need to store all possible open connections for the same user id. After this I can iterate and send messages to all open connections for same user.
The above HashMap only stores each user id and connection once. I need to get one key with multiple values. How can I make the value into a list or an array, so I can see which connections exist and send to them all?
I am not talking about different value types, like enums. I am talking about the same type values but more than one. Maybe HashMap is not designed for this?
Alternative ideas are also welcomed.
To do this with a HashMap you should use a Vec as the values, so that each key can point to multiple Senders. The type then would be HashMap<u32, Vec<Sender>>.
Using this structure, just using insert() can get clunky when you need to mutate the values like this, but instead you can use the Entry API for retrieving and updating records in one go. For example:
let mut hash_map: HashMap<u32, Vec<Sender>> = HashMap::new();
hash_map.entry(3)
// If there's no entry for key 3, create a new Vec and return a mutable ref to it
.or_default()
// and insert the item onto the Vec
.push(sender);
You could also use the multimap crate, which does something similar under the hood, but adds a layer of abstraction. You might find it easier to work with:
let mut multi_map = MultiMap::new();
multi_map.insert(3, sender_1);
multi_map.insert(3, sender_2);
The method multi_map.get(key) will the first value with that key, while multi_map.get_vec(key) will retrieve all of them.