---
name: "mtbl_fileset"
section: "3"
platform: "linux"
package: "libmtbl-dev"
version: "1.6.1-1+b1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/mtbl_fileset"
---

# mtbl\_fileset(3)

automatic multiple MTBL data file merger

## NAME

mtbl\_fileset - automatic multiple MTBL data file merger

## SYNOPSIS

**#include \<mtbl.h\>**

Fileset objects:

```
struct mtbl_fileset *
mtbl_fileset_init(const char *fname, const struct mtbl_fileset_options *fopt);
```

```
struct mtbl_fileset *
mtbl_fileset_dup(struct mtbl_fileset *orig, const struct mtbl_fileset_options *fopt);
```

```
void
mtbl_fileset_destroy(struct mtbl_fileset **f);
```

```
void
mtbl_fileset_reload(struct mtbl_fileset *f);
```

```
void
mtbl_fileset_reload_now(struct mtbl_fileset *f);
```

```
const struct mtbl_source *
mtbl_fileset_source(struct mtbl_fileset *f);
```

```
void
mtbl_fileset_partition(struct mtbl_fileset *f,
                mtbl_filename_filter_func cb,
                void *clos,
                struct mtbl_merger **m1,
                struct mtbl_merger **m2);
```

Fileset options:

```
struct mtbl_fileset_options *
mtbl_fileset_options_init(void);
```

```
void
mtbl_fileset_options_destroy(struct mtbl_fileset_options **fopt);
```

```
void
mtbl_fileset_options_set_merge_func(
        struct mtbl_fileset_options *fopt,
        mtbl_merge_func fp,
        void *clos);
```

```
void
mtbl_fileset_options_set_dupsort_func(
        struct mtbl_fileset_options *fopt,
        mtbl_dupsort_func fp,
        void *clos);
```

```
void
mtbl_fileset_options_set_filename_filter_func(
        struct mtbl_fileset_options *fopt,
        mtbl_filename_filter_func fp,
        void *clos);
```

```
void
mtbl_fileset_options_set_reader_filter_func(
        struct mtbl_fileset_options *fopt,
        mtbl_reader_filter_func fp,
        void *clos);
```

```
void
mtbl_fileset_options_set_reload_interval(
        struct mtbl_fileset_options *fopt,
        uint32_t reload_interval);
```

## DESCRIPTION

The **mtbl\_fileset** is a convenience interface for automatically maintaining a merged view of a set of MTBL data files. The merged entries may be consumed via the [**mtbl\_source**(3)](/mtbl_source/3.md) and [**mtbl\_iter**(3)](/mtbl_iter/3.md) interfaces.

**mtbl\_fileset** objects are initialized from a "setfile", which specifies a list of filenames of MTBL data files, one per line. For each filename, if it is not an absolute path, then the directory name of the fileset file’s pathname is prepended to it. Examples: If the setfile path is "/export/dnstable/mtbl/dns.fileset", and a line in it is of the form "dns.2017.Y.mtbl" then **dnstable** will try to open "/export/dnstable/mtbl/dns.2017.Y.mtbl". If the setfile path is "/export/dnstable/mtbl/dns.fileset", and a line in it is of the form "/tmp/dns.2017.Y.mtbl" then **dnstable** will try to open "/tmp/dns.2017.Y.mtbl".

Internally, an **mtbl\_reader** object is initialized from each filename and added to an **mtbl\_merger** object. The setfile is watched for changes and the addition or removal of filenames from the setfile will result in the corresponding addition or removal of **mtbl\_reader** objects.

Because the MTBL format does not allow duplicate keys, the caller must provide a function which will accept a key and two conflicting values for that key and return a replacement value. This function may be called multiple times for the same key if the same key is inserted more than twice. See [**mtbl\_merger**(3)](/mtbl_merger/3.md) for further details about the merge function.

**mtbl\_fileset** objects are created with the **mtbl\_fileset\_init**() function, which requires the path to a "setfile", *fname*, and a non-NULL *fopt* argument which has been configured with a merge function *fp*. **mtbl\_fileset\_source**() should then be called in order to consume output via the [**mtbl\_source**(3)](/mtbl_source/3.md) interface.

The **mtbl\_fileset\_dup**() function, which requires a **mtbl\_fileset** object and a non-NULL **opt** argument, creates a duplicate **mtbl\_fileset** object that shares the underlying fileset, but with different fileset options, as specified.

Accesses via the [**mtbl\_source**(3)](/mtbl_source/3.md) interface will implicitly check for updates to the setfile. However, it may be necessary to explicitly call the **mtbl\_fileset\_reload**() function in order to check for updates, especially if files are being removed from the setfile and the **mtbl\_source** is infrequently accessed.

The **mtbl\_fileset\_reload**() function avoids checking for updates more frequently than every *reload\_interval* seconds. If **reload\_interval** is set to **MTBL\_FILESET\_RELOAD\_INTERVAL\_NEVER**, then **mtbl\_fileset\_reload**() function will only load the fileset once. The **mtbl\_fileset\_reload\_now**() function can be called to bypass the *reload\_interval* check.

The **mtbl\_fileset\_partition**() function yields two **struct mtbl\_merger** objects that are split based on the output of a callback. The caller is responsible for calling **mtbl\_merger\_destroy**() on each of these mergers. Calls to **mtbl\_source\_\***() on the fileset’s source object, and calls to **mtbl\_fileset\_reload**() and **mtbl\_fileset\_reload\_now**(), including those implicitly performed by operations on the fileset source, may leave these mergers in an inconsistent state. For this reason, **mtbl\_fileset\_partition**() use is deprecated in favor of **mtbl\_fileset\_dup**() with the **fname\_filter\_func** option set.

### Fileset options

**merge\_func**

See [**mtbl\_merger**(3)](/mtbl_merger/3.md). An **mtbl\_merger** object is used internally for the external sort.

**dupsort\_func**

See [**mtbl\_merger**(3)](/mtbl_merger/3.md). Used to sort the entries with duplicate keys during the merge process based on their data.

**fname\_filter\_func**

Used to filter specific files by name from a fileset. If the function returns **false**, the file’s data will not be included in the results returned by any iterators on the fileset.

**reader\_filter\_func**

Used to filter specific readers from a fileset. If the function returns **false**, the reader’s data will not be included in the results returned by any iterators on the fileset.

**reload\_interval**

Specifies the interval between checks for updates to the setfile, in seconds. Defaults to 60 seconds. **MTBL\_FILESET\_RELOAD\_INTERVAL\_NEVER** is a special value that indicates to never reload the fileset.