OVERVIEW

This technical log contains the story about how this module in apprentice I did an asportation in serializing and deserializing some pages. The serialization logic already existed, but my work consisted of translating everything into another. document based on another module that was did these changes. You'll see my communication with the owners and the kind of issues I had to develop this assignation. Finally, I'll give you a conclusion about these issues.

CONTEXT

SirixDB is an embeddable, temporal, evolutionary database system, which uses an append-only approach to store immutable revisions. It keeps the full history of each resource. Every commit stores a space-efficient snapshot through structural sharing. It is log-structured and never overwrites data. SirixDB uses a novel page-level versioning approach. Github Sirix project

When I chose this issue I had in mind that serialization/ deserialization sounds like something easy that I could understand. Also, it motivated me that already existed an example in the same project. I'm glad that wasn't as easy as I thought. It brought me out of my conform zone trying to communicate for understanding the project, learning new concepts, and for sure debbuging to find errors.

DEVELOPMENT

>Set Up

My first step was to install the repository and understand its constitution. There my first incident happened because I had some trouble making run the project. I used grandle because I saw some files in the repository and instructions in README file. However, the project was failing when I tried to run it. I also, see some files of maven so I tried to change to use maven, but I think they had a recent migration from maven to grandle, so again I change to grandle. The next photo shows you the message when the project fail running.

I spend a day trying to figure out why my IDEA was taking version 17 when I already had version 19 installing. I had both versions installed in my IDE. The solution was to delate version 17. I tried to change the configurations but still, it didn't want to take the 19 for default.

Then, I start looking to the folders and modules to understand how they were build and connecte. My changes had to be on page folder but this was connected with node, and both were part of sirix-core module. The project had 9 modules, that means that it was the first big project I have seen.

Inside Page folder, there are all the pages that I need to serialize/deserialize. The configuration already have the serialized and deserialized but they were in the constructor and in a method named serialize from an interface named Page.

Something difficult that I had to overcome was the nervousness to make questions to the owners. The context of the issues had some details that I couldn't understand but I wasn't sure if that was because I'm naive or if an experienced programmer could do the issue with only that information. Then, I asked some people close to me for a guide about what to do, how to start, and where to look for answers.
That really made me feel out of my comfort zone. Later, I realized that I had to ask questions for the owner if I want to understand the issue and the project. I did it and I received the first explication of my issue that you can see in the next picture.

That question came from my trying to understand how the serialize and deserialization was already made in the pages folder, because It was already there but I didn't understand what kind of changes I need to do it on the folders if the configuration was done.

I received a good response from the owners because they where answering my questions and helping me understanding the project.

>Changes

I started making changes on PageKind which was an enum. The objective was to have a serialize and deserialize method for every page. They already existed but they only call the inside method in the page and the constructor.

The next pictur is the logic that was in the serialization method for one of the pages. Every page had different logic but some of them were similar. The point of showing you this old code is that you (reader) have an idea about the reason for the new changes. For the deserialization changes, they were in the constructor of each page. I'll show it later.

Something I noticed, and I told the owner, of some errors in the existing logic. For example, I point in the last picture the line 143 which should have currentMaxLevelOfIndirectPagesMap.size() instead of maxNodeKeys.size(). He told me that it was a mistake.

I started the changes in the PageKind on CASPage. In the picture below, you'll see the new code that I adapted it here in the enum. I had a mistake that I would discover later. The owner wanted to delete the serialize method from the Page interface. That means 224 line was wrong. I had to serialize the delegate page in a different way. But at this point, I didn't know that. I still was trying to understand the code, and what meant those lines. Also, I didn't catch that he wants to delate the serialize method from Page.

For the deserialization was something similar, I just changed the construction logic and made everything in PageKind, then I started the new page just sending the new data as attributes.

When I did the first page I continued making the changes for the others. In total 10 pages more to change the logic to pageKing. If all of them were similar I would have finished faster, but there were a couple of them that were complicated and large. For example, KeyValueLeftPage was the most difficult to change. It has some delegates different than other pages. here check the changes in KeyValueLeftPage

When I did make the changes for serialize/deserialize, I look for a way to test my code. I asked the owner if he had some tests. I did the test in the sirix-core module. All of them failed. I knew they could fail, but I was nervous about how to find the mistakes because I had some doubts about logic. I started asking the owner what he belived. He suggested making debugging to know why it failed. It probably was in my new methods, also he asked me to delete the serialize method from Page. At the first moment, my failed test where because I deleted that method and it was used in other places of the core module. Then, I was stuck in the section where the fail redirected me to my new methods. I decided it was because I had something missed form the old serialization. After few days working on it, I descovered was the delegates!! I deleted them after I deleted the serialize method from Page. I thought they weren't important because I had the idea that the delegate was the serialization code I translated. You can check the second picture below in line 121. I thought it meant the serialized method on the specific page but it was more than that.

I got the conclusion that my final errors came from my serialization because I found that some references weren't initialized. A value -15 is a default value when they haven't stared.

I took one and a half days to develop a way to serialize the delegate from every page because every page could have a different delegate and also more than one. I did another global method in PageKind to use on every Page that has the possibility to serialize with different delegates. At that point, I received a suggestion from the owner. He told me to use a switch. I was confused about how to make the delegate serialization if we didn't have the serialize method from the page. There the idea of a global method was suggested and he liked the idea.

I fixed that mistake but I still had another bug somewhere because the test didn't pass, but the error was different so that was good. I got stuck a little looking for where that mistake come. I already have an idea from RecordPage, one of the complicated pages that I changed. With debugging, I realized that in that point the data was lost after a deserialization, the "source" attribute that contained the data serialized got empty in the middle of the deserialization. I wasn't sure why that happened. So I asked the owner for a hint haha, a light in the tunnel. Then he asked, are you sure that all the logic is copied in the same sequence? There I remembered that I changed a declaration of variables in the deserialization. They were between the code but I set that variable at the start of the method. The owner didn't have any idea that it was the problem but his experience told me a clue to find in my memory the answer. Finally, I did the changes and the test started passing.

We were so exited that we already had this overcome. The owner told me that this was important for his project. He was interested that I finish this issue for future changes that he wants to make in this project. I share below a photo of a comment he made to me when I started conversation to understand this issue.

After pull request

After I did my pull request in March 8th, I felt happy because it was just at time to tried a new eassy issue in another repository. Nevertheless, my PR fail the boot tests. Actually it failed just one. I didn't try that test before because I wasn't awared it existed.

I debugged the code to check what was happening. I decided to use a comparison between a code without changes and the one that was failing.

Comparation

Code failing test

Good Code passing test

I found a difference that affected the binarySearch. The bug was making the test fail because it has a different revision number. Why this number is different? , it was the question I searched March 9th all day.

I couldn't reach with the right answer, but I was pretty close. I planned to check the serialization of a page named UberPage, because this reference was set there. Also, it was related with RevisionRootPage. I left the search for the next day because I felt petty sad because my deadline to finish this Open Source module was March 10th. I send my findings to the owner to see what he says for the next morning. Then, He answered with the commenst tha you see in the next photo:

I was so grateful for his help because I felt really sad I couldn't finish on time where was the bug. At the end, I finished at time and the owner was happy with the results of my changes.

Conclusion

This project taught me a lot about the serialization/ deserialization of data. Also, I practice my communication skills. That was pretty tough to accomplish because I felt shame for my questions on the issue.

In the end, I was really proud that the owner invite me to collaborate again on his project. I told him that I really want to continue learning about DB and Java programming. This make me feel confortable with this issue because I felt lost when I start and then I gain some confident.