# Systematic Literature Review of Challenges in Blockchain Scalability
## 6 RQ1: How Scalability Issue Can Impact Blockchain Implementation? Blockchain was made famous by Bitcoin in 2008 [2], and since then it has already advanced into several industries. There are claims that blockchain is the technology that will disrupt the technology eco-system. However, it is yet to witness much growth and disruption apart from cryptocurrency. Figure 7 is about public blockchain applications except cryptocurrency. From our SLR, cryptocurrency (Bitcoin and Ethereum) is noted as the state-of-the-art application of public blockchains. Next to cryptocurrency, IoT is the most discussed blockchain-related application, with 17 publications. Our findings also revealed that although blockchain is very applicable to IoT applications, it is yet to achieve the preferred outcomes due to scalability issues. Blockchain appeared to be influencing  
Figure 5: Figure illustrates the analysis of selected paper types in the blockchain domain. Figure 6: Figure illustrate the analysis of geographic distribution of selected paper in the blockchain domain. and disrupting many other industries such as finance, resource management, healthcare, education, and agriculture [17]. Every selected paper discusses and states that scalability is a critical issue in public blockchains. These papers manifested the fact that blockchain is yet to be able to \"scale-up\" at par to the centralized infrastructure, be it in cryptocurrency or some other applications. Scalability in public blockchains is recognized as the vital issue that is affecting the performance and efficiency in the blockchain associated applications. The following section discusses the scalability issue based on the consolidated data from the articles reviewed. This is to justify the impact of scalability in the top three public blockchain-associated applications, namely, Bitcoin, Ethereum, and IoT. Scalability Issue in Major Public Blockchains Application (Bitcoin and Ethereum)  
The high acceptance of cryptocurrency is escalating the burning scalability issue in public blockchains [6; 7; 28]. The number of transactions with Bitcoin and Ethereum is increasing every day [5; 7]. More 13,000 transactions take place with Bitcoin everyday [7]. This high number of transactions is making Bitcoin transactions bulky. One of the processes in public blockchains is to verify the source of the transaction, and every node needs to store and validate every transaction. It is therefore a challenge to the miners to verify every transaction in Bitcoin as it scales up in volume. This is happening because of the inefficient proof-of-work (PoW) [29] consensus mechanism deployed in the Bitcoin in verifying and validating every single transaction. PoW is unfortunately the most frequently used consensus protocol [17]. It is worth to notice that the total number of transactions in Ethereum has continuously grown over the years [7]; many thousands of transactions have occurred every day in recent years. In Ethereum, the limited block size cannot accommodate all the transactions submitted by the miners. It is therefore challenging for the miners to verify every transaction. The consequence is that the miners tend to select transactions with more rewards for the sake of securing more rewards. The transactions  
Figure 7: Blockchain application domain per selected papers. with fewer rewards are left in the queue, leading to longer transaction latency [30]. It is estimated that more than 10 k transactions are waiting to be verified. The highest transaction throughput in Bitcoin is capped at 7 TPS (Transaction-per-second). In contrast to the VISA counterpart, 400 TPS is the norm [5; 6; 29; 30; 31] The block interval latency (in public blockchains) is in a magnitude of up to 10 min [32] for a transaction to be verified. Ethereum was to be theoretically verified at the rate of 1k TPS, but due to certain limitations in its structure, is more likely to be verified at 20 TPS. This is far less than other electronic payment methods such as PayPal--at 193 TPS.