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title: "Terms" |
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--- |
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# Terms |
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### Snapshot |
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A **snapshot** is the state of a table at some time. |
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Each snapshot lists all of the data files that make up the table's contents at the time of the snapshot. Data files are stored across multiple [manifest](#manifest-file) files, and the manifests for a snapshot are listed in a single [manifest list](#manifest-list) file. |
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### Manifest list |
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A **manifest list** is a metadata file that lists the [manifests](#manifest-file) that make up a table snapshot. |
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Each manifest file in the manifest list is stored with information about its contents, like partition value ranges, used to speed up metadata operations. |
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### Manifest file |
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A **manifest file** is a metadata file that lists a subset of data files that make up a snapshot. |
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Each data file in a manifest is stored with a [partition tuple](#partition-tuple), column-level stats, and summary information used to prune splits during [scan planning](docs/latest/performance.md#scan-planning). |
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### Partition spec |
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A **partition spec** is a description of how to [partition](docs/latest/partitioning.md) data in a table. |
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A spec consists of a list of source columns and transforms. A transform produces a partition value from a source value. For example, `date(ts)` produces the date associated with a timestamp column named `ts`. |
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### Partition tuple |
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A **partition tuple** is a tuple or struct of partition data stored with each data file. |
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All values in a partition tuple are the same for all rows stored in a data file. Partition tuples are produced by transforming values from row data using a partition spec. |
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Iceberg stores partition values unmodified, unlike Hive tables that convert values to and from strings in file system paths and keys. |
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### Snapshot log (history table) |
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The **snapshot log** is a metadata log of how the table's current snapshot has changed over time. |
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The log is a list of timestamp and ID pairs: when the current snapshot changed and the snapshot ID the current snapshot was changed to. |
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The snapshot log is stored in [table metadata as `snapshot-log`](spec.md#table-metadata-fields). |
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