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Add posting index and covering index documentation #404

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Add posting index and covering index documentation
nwoolmer Mar 30, 2026
1527456
Update posting/covering index docs to match current codebase
nwoolmer Apr 10, 2026
72b98ca
Add posting index docs to explain, symbol, mat-view, config pages
nwoolmer Apr 10, 2026
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Clarify encoding trade-offs: delta vs adaptive modes
nwoolmer Apr 10, 2026
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Add EF encoding as distinct option, clarify all three modes
nwoolmer Apr 10, 2026
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17 changes: 15 additions & 2 deletions documentation/concepts/deep-dive/indexes.md
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Expand Up @@ -14,6 +14,16 @@ Indexing is available for [symbol](/docs/concepts/symbol/) columns in both table
and [materialized views](/docs/concepts/materialized-views). Index support
for other types will be added over time.

QuestDB supports two index types:

| Index type | Syntax | Covering support | Best for |
|------------|--------|-----------------|----------|
| **Bitmap** (default) | `INDEX` or `INDEX TYPE BITMAP` | No | General-purpose, low write overhead |
| **Posting** | `INDEX TYPE POSTING` | Yes (via `INCLUDE`) | Read-heavy workloads, selective queries, wide tables |

See [Posting index and covering index](/docs/concepts/deep-dive/posting-index/)
for the detailed guide on the posting index and its covering query capabilities.

## Index creation and deletion

The following are ways to index a `symbol` column:
Expand Down Expand Up @@ -97,6 +107,9 @@ Consider the following query applied to the above table

:::warning

Index capacity applies to **bitmap indexes only**. Posting indexes manage
their own storage layout and do not use this setting.

We strongly recommend to rely on the default index capacity. Misconfiguring this property might
lead to worse performance and increased disk usage.

Expand All @@ -114,8 +127,8 @@ When in doubt, reach out via the QuestDB support channels for advice.

:::

When a symbol column is indexed, an additional **index capacity** can be defined
to specify how many row IDs to store in a single storage block on disk:
When a symbol column has a bitmap index, an additional **index capacity** can be
defined to specify how many row IDs to store in a single storage block on disk:

- Server-wide setting: `cairo.index.value.block.size` with a default of `256`
- Column-wide setting: The
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