> ## Documentation Index > Fetch the complete documentation index at: https://support.entegrata.com/llms.txt > Use this file to discover all available pages before exploring further. # Sync Strategies > Understand Overwrite, Overlay, and Merge, and choose the right strategy for each sync ## Overview Choosing a strategy is the one decision in a sync that matters most, so it's worth understanding before you click anything. Sync compares the source and the target **as they are right now**. It has no memory of who changed what, or when — so it can't guess your intent. Your strategy choice *is* the intent. Every difference Sync finds falls into one of three buckets, and each strategy handles those buckets differently: | The difference | Overwrite | Overlay | Merge | | ------------------------------------ | ------------------------------- | ------------------------------- | ---------- | | In the source, **not** in the target | Added | Added | You choose | | In both, but **different** | Target takes the source's value | Target takes the source's value | You choose | | In the target, **not** in the source | **Deleted** | Left alone | You choose | ## Overwrite *"Make the target match the source."* The target ends up an exact copy of the source's mapping configuration. Anything in the target that doesn't exist in the source is **deleted**. **Overwrite is destructive.** Mappings in the target pipeline that don't exist in the source will be deleted. Use it when the source is unambiguously the truth — resetting a test pipeline from main, or syncing a test pipeline you know is complete. Don't use it on production if production contains mapping work that isn't also on your test pipeline. Overwrite is the default strategy when you open the Sync dialog. ## Overlay *"Add and update, never delete."* Everything new or changed in the source lands in the target. Anything the target has on its own stays exactly where it is. This is the safe choice for the common case: you added three fields on a test pipeline and want them in production, and you don't want to risk anything else. Overlay **cannot express a deletion.** If you deliberately removed a field on your test pipeline and want it gone from production too, Overlay won't do it — use Merge or Overwrite. When Overlay finds an entity that only the target has, it leaves it alone and reports it as **Skipped** in the sync result. ## Merge *"Show me every difference and let me decide."* Merge walks you through the differences one entity at a time, and within each entity, one item at a time. For each one you either accept the suggested change or leave the target alone. **Nothing is applied until you commit.** This is the precise option — slower, but you see and approve everything. It's also the only strategy that lets you mix decisions: bring two fields across, leave a third, and remove a fourth, all in a single pass. Walk through the Merge review wizard step by step ## Choosing a Strategy | Your situation | Use | | --------------------------------------------------------------------- | ------------- | | Test pipeline is complete and should replace production wholesale | **Overwrite** | | Resetting a drifted test pipeline from main | **Overwrite** | | Adding new fields or entities to production, removing nothing | **Overlay** | | You're not sure what's in the target and don't want to risk deletions | **Overlay** | | Real work has happened on *both* pipelines | **Merge** | | You need to delete something from the target, but not everything | **Merge** | | You want to review every difference before anything is written | **Merge** | When you select a strategy in the Sync dialog, a matching banner confirms what it will do — read it before you continue. It's the last checkpoint before a destructive change. ## Related Topics What Sync is and where to find it Apply a strategy to one entity Apply a strategy to a whole pipeline See the differences before choosing