When HBase write data is executed in the Fusionlnsight HD system, the data is written to the memory MemStore, the log HLog, and the HDP

In the HBase write process within Huawei FusionInsight HD, data is first written to the Write-Ahead Log (HLog). This is a crucial step that ensures data durability and prevents data loss. The HLog is a commit log stored on HDFS. Only after the data is successfully written to the HLog is it then added to the MemStore, which is an in-memory write buffer. The client receives confirmation of a successful write only after the HLog entry is secured. This sequence guarantees that if a RegionServer fails before the MemStore is flushed to a permanent HFile, the data can be recovered by replaying the HLog.

A. MemStore: Data is written to the MemStore after the HLog write. It is an in-memory structure and does not provide durability on its own.
C. HDFS: HDFS is the underlying distributed file system where HLog and HFiles are stored, not the immediate logical component that receives the initial write for durability.
D. Memory: This is a general term. MemStore is the specific HBase component residing in memory, but the write to the persistent HLog precedes the in-memory write.

1. Apache HBase™ Reference Guide. (Version 2.4.9, Section 11.7. Write Path). The official documentation states, "When a client issues a Put operation, the first step is to write the data to the write-ahead log (WAL)... After the data is written to the WAL, it is placed in the MemStore." This confirms the sequence where HLog (WAL) is written first for durability.

2. Huawei FusionInsight HD 6.5.1 Product Documentation. (Section: HBase Technical Principles > HBase Read/Write Process). The documentation details the write process: "To write data... the RegionServer first writes the data to HLog to ensure that the data is not lost. Then, the RegionServer writes the data to the MemStore." This directly supports that the HLog write is the primary step for data safety.

3. "HBase in Action" by Nick Dimiduk and Amandeep Khurana. (Chapter 2, Section 2.2.2. Write-ahead Log). This authoritative book explains, "Before any data is written to the MemStore, HBase writes the update to the WAL... This mechanism protects the data from being lost in the event of a RegionServer failure." This reinforces the HLog-first principle for data protection.