1# Data Management Development 2 3## How Do I Save PixelMap Data to a Database? 4 5Applicable to: OpenHarmony SDK 3.2.3.5 6 7You can convert a **PixelMap** into an **ArrayBuffer** and save the **ArrayBuffer** to your database. 8 9Reference: [readPixelsToBuffer](../reference/apis/js-apis-image.md#readpixelstobuffer7-1) 10 11## How Do I Obtain RDB Store Files? 12 13Applicable to: OpenHarmony SDK 3.2.3.5, stage model of API version 9 14 15Run the hdc_std command to copy the .db, .db-shm, and .db-wal files in **/data/app/el2/100/database/*bundleName*/entry/db/**, and then use the SQLite tool to open the files. 16 17Example: 18 19``` 20 hdc_std file recv /data/app/el2/100/database/com.xxxx.xxxx/entry/db/test.db ./test.db 21``` 22 23## Does the Database Has a Lock Mechanism? 24 25Applicable to: OpenHarmony SDK 3.2.5.5, stage model of API version 9 26 27The distributed data service (DDS), relational database (RDB) store, and preferences provided OpenHarmony have a lock mechanism. You do not need to bother with the lock mechanism during the development. 28 29## What Is a Transaction in an RDB Store? 30 31Applicable to: all versions 32 33When a large number of operations are performed in an RDB store, an unexpected exception may cause a failure of some data operations and loss of certain data. As a result, the application may become abnormal or even crash. 34 35A transaction is a group of tasks serving as a single logical unit. It eliminates the failure of some of the operations and loss of associated data. 36 37## What Data Types Does an RDB Store Support? 38 39Applicable to: OpenHarmony SDK 3.0 or later, stage model of API version 9 40 41An RDB store supports data of the number, string, and Boolean types. The number array supports data of the Double, Long, Float, Int, or Int64 type, with a maximum precision of 17 decimal digits. 42 43## How Do I View Database db Files? 44 45Applicable to: OpenHarmony SDK 3.2.6.5, stage model of API version 9 46 471. Run the **hdc_std shell** command. 48 492. Obtain the absolute path or sandbox path of the database. 50 51The absolute path is **/data/app/el2/<userId>/database/<bundleName>**. The default **<userId>** is **100**. 52 53To obtain the sandbox path, run the **ps -ef | grep hapName** command to obtain the process ID of the application. 54 55The database sandbox path is **/proc/<Application process ID>/root/data/storage/el2/database/**. 56 573. Run the **find ./ -name "\*.db"** command in the absolute path or sandbox path of the database. 58 59## How Do I Store Long Text Data? 60 61Applicable to: OpenHarmony SDK 3.2.5.5, API version 9 62 63- Preferences support a string of up to 8192 bytes. 64 65- The KV store supports a value of up to 4 MB. 66 67Reference: [Preference Overview](../database/database-preference-overview.md) and [Distributed Data Service Overview](../database/database-mdds-overview.md) 68 69## How Do I Develop DataShare on the Stage Model 70 71Applicable to: OpenHarmony SDK 3.2.5.5, API version 9 72 73The DataShare on the stage model cannot be used with the **DataAbility** for the FA model. The connected server application must be implemented by using **DataShareExtensionAbility**. 74 75Reference: [DataShare Development](../database/database-datashare-guidelines.md) 76 77