1. Why do I need to submit the fee_limit field when sending a transaction to call a smart contract？

Answer
Prevent the contract call transaction from consuming too much energy.

Explanation
The fee_limit indicates the value of the total energy that a contract caller can tolerate at most for this transaction. The base unit is sun, and the maximum value can be set to 1e10. If the user does not set fee_limit, the default value is 0. For example, if the fee_limit is set to 1000 sun in the transaction, it means that the contract caller will endure the transaction and consume up to 1000/280 energy (the current unit price of energy is 280 sun).

If the amount of energy consumed by the transaction execution exceeds the fee_limit*energy unit price, contract execution will be stopped and an OUT_OF_ENERGY error will be triggered.

In some contract functions, there will be complex loops. If the user calls it by mistake without knowing it, it may cause the user to consume too much energy, so the user can set this fee_limit field as an upper limit.

There are some situations which cause all fee_limit to be deducted:

• Illegal instruction encountered during contract execution
• Contract call timeout, trigger OUT_OF_TIME error
• if the array index you are accessing is too large or negative (for example x[i] where i >= x.length or i < 0).
• If you access a fixed length of bytesN the index is too large or negative.
• If you use zero as a divisor for division or modulo operations (for example 5 / 0 or 23 % 0 ).
• If you shift the negative digit.
• If you convert a too large or negative value to an enum type.
• If you call an uninitialized internal function type variable.
• If you call the argument of the assert (expression), and the final result is false.
• If a JVMStackOverFlowException occurs.
• If an OutofMem exception occurs, that is, memory exceeded 3M.
• During contract operation, an overflow occurs, such as addition.

2. Why would I trigger OUT_OF_TIME error when calling contract function?

Answer
The contract function is too complex or the performance of the SR node fluctuates.

Explanation
At present, TRON has a global setting. The execution time of calling smart contract transactions cannot exceed 80ms. This 80ms parameter can be modified by SR voting. If the contract code is very complex and the execution time exceeds 80ms, it will trigger an OUT_OF_TIME error and deduct all fee_limit fees.

If the same contract function sometimes triggers the OUT_OF_TIME error, sometimes it does not trigger the OUT_OF_TIME error, indicating that the complexity of the contract code is at a critical value. Because the machine performance of different SRs is different, it will cause intermittent triggering.

In addition, it should be noted that due to the fluctuation of SR machine performance, there will be a small probability that the contract function call with very low complexity will also trigger the OUT_OF_TIME error. It is recommended that users set the appropriate fee_limit according to the contract complexity to prevent excessive losses caused by excessive setting of fee_limit.

3. What is the destruction address of TRON?

Destruction address is the address that is not controlled by anybody, that is, no one has the private key of the address. For example, address 0, address 1, address 2... These special addresses can all be used as destruction address.

4. How to troubleshoot when calling the contract and return the revert error?

Answer

1. First, according to txid, query the contractResult field in the result returned through the wallet/gettransactioninfobyid interface. If the field is not empty, you can see the abi code value of the message, convert the code value into a string, and find the reason for the error.
   For example, txid:e5e013e81cb50a4c495a11c8130ad165a4e98d89b9e3fb5b79e6111bf23b31ed
   Return contractResult data:
   "contractResult": [
   "08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001e536166654d6174683a207375627472616374696f6e206f766572666c6f770000"
   ]
   Converting 1e536166654d6174683a207375627472616374696f6e206f766572666c6f77 into a string is: SafeMath: subtraction overflow, this transaction is because the transfer address overflowed during the subtraction operation during the transfer. The specific failure may be caused by insufficient balance. You need to check the address balance and transfer amount，Other errors can be checked according to the specific reason of the error.

2. If the contractResult is empty, it may be caused by the failure of the require assertion without message in the contract. For details, please refer to the document and view the contract source code for analysis.

5. How to calculate the bandwidth and energy consumed when calling the contract?

Answer

1. The bandwidth is calculated based on the number of bytes encoded by the transaction protobuf.
2. Energy is deducted based on the instructions executed by the contract. Different instructions are deducted differently. The more complex the contract, the more energy will be consumed. The energy consumed by the current contract can be estimated by testing on the testnet or viewing the previous historical calls of the contract through tronscan, or invoking API.
   Resource model can refer to the document

How to estimate the energy consumption through API invoking
From GreatVoyage-v4.3.0(Bacon), user can invoke the readonly method as well as the non-readonly method of a contract via wallet/triggerconstantcontract API, and there is a new field energy_limit in wallet/triggerconstantcontract return value, it means the actual energy consumption of this contract invoking.
Please pay attention: This operation will not generate an on-chain transaction, nor will it change the status of the current node. Invoking non-readonly method can be used to forecast the energy usage.

6. After the transaction broadcast is successful, why can't it be queried on the chain?

Answer
The transaction broadcast is successful but not on the chain because the transaction is not broadcast to the SR node because of the node's network or other unknown reasons. In this case, because the transaction has a validity period, it is best to add a delay judgment, and add it after the transaction validity period. If a little extra time is not on the chain, it can be judged that the transaction has exceeded the validity period, and the transaction can be initiated again, or the transaction can be rebroadcast within the validity period.

7. How to solve "OUT_OF_ENERGY" error?

Answer

1. It is necessary to check whether the address of the calling contract has TRX and whether it is enough to pay for the burning energy or bandwidth cost, otherwise the address needs to obtain enough TRX.
2. If there is enough TRX, the feelimit set by the transaction is smaller, and the feelimit setting needs to be increased.

8. How to solve the problem of slow node block synchronization or stop synchronization?

Answer
1.Improve machine configuration, recommend 16core 32GRAM 1T hard drive (ssd)

In the result of the following command, the maximum value of both cpu cores and siblings needs to be greater than or equal to 16.

$cat /proc/cpuinfo | grep -e "cpu cores" -e "siblings" | sort | uniq
cpu cores : 8
siblings : 16
2.Increase the time tolerance of verification transactions
Increase the value of the maxTimeRatio configuration item in the node configuration file to 20.0 or higher.

vm = {
supportConstant = false
minTimeRatio = 0.0
maxTimeRatio = 20.0
saveInternalTx = false
}
3.Modify java-tron startup parameters to increase parallel garbage collection parameters：XX:+UseConcMarkSweepGC and -Xmx
like:
java -Xmx24g -XX:+UseConcMarkSweepGC -jar FullNode.jar -c .....
-XX:+UseConcMarkSweepGC should be placed before the -jar parameter, not at the end
-Xmx can be set to 80% of physical memory

9.How to solve SERVER_BUSY error?

Answer
If the number of unprocessed transactions of the node exceeds 2000, a server busy error will be returned. According to the machine situation, you can increase the PendingSize by modifying the node.maxTransactionPendingSize in the node configuration file. For example, set node.maxTransactionPendingSize = 5000.

10.How to solve the error of TronGrid 503 Service Temporarily Unavailable?

Answer
Because TronGrid currently has an IP frequency limit for all TronGrid requests, the IP frequency is limited to 15QPS for TronGrid HTTP requests that use API Key. For TronGrid HTTP requests that without API Key, the current IP frequency is limited to 10QPS and will gradually decrease periodically. The current IP frequency limit for using the TronGrid GRPC service is 15QPS. If the frequency limit is exceeded, a 503 error will be returned. If a 503 error is reported, please reduce the frequency of the TronGrid request and it is recommended to add an API Key as soon as possible.

11. How to solve no Constant_result in the transaction when user triggers the pure or view methods of the contract.

Answer
This issue is currently only seen when users downgrade the java-tron version from GreatVoyage-v4.2.2 (Lucretius) or other higher versions to GreatVoyage-v4.2.1 (Origen) (or GreatVoyage-v4.2.0 (Plato)). If users encounter this problem, they need to use a repair tool to repair the database. After the repair is complete, users can use GreatVoyage-v4.2.2.1 (Epictetus) or later versions to start the node normally. Please refer to the detailed operation steps from DBReqair.jar User Guide

12. Broadcast Response Code

CONTRACT_VALIDATE_ERROR Common Error Messages Description

13. How to speed up the node startup process？

Answer
From GreatVoyage-v4.3.0(Bacon), if the node adopts LevelDB, user can use the levelDB startup optimization tool to improve the node startup speed. This tool optimizes the file size of the manifest and the startup process of LevelDB, that will reduce memory usage, and improve node startup speed. The detailed steps please refer to LevelDB startup optimization tool - user guide

14.How to use tronWeb to invoke contract whose ABI is not on the chain?

Answer
Please refer to the document: How to use tronWeb to invoke contract whose ABI is not on the chain

15.How to judge the funds transferring in and out of an address by scanning the block?

Answer
For exchange or wallet, it is usually necessary to obtain historical transaction information of an account, or to monitor the real-time transfer of funds from an account address. The exchange or wallet can build a full node, and then obtain the transaction records of the account address by parsing historical blocks, for more details please refer to here.