Isolation during flushing and merging

When flushing and compacting a real-time table Manticore provides isolation, so that a changed state doesn't affect the queries that were running when this or that operation started.

For instance, while compacting a table we have a pair of disk chunks that are being merged and also a new chunk produced by merging those two. Then, at one moment we create a new version of the table, where instead of the original pair of chunks the new one is placed. That is done seamlessly, so that if there's a long-running query using the original chunks, it will continue seeing the old version of the table while a new query will see the new version with the resulting merged chunk.

Same is true for flushing a RAM chunk: we merge all suitable RAM segments into a new disk chunk, and finally put a new disk chunk into the set of disk chunks and abandon the participated RAM chunk segments. During this operation, Manticore also provides isolation for those queries that started before the operation began.

Moreover, these operations are also transparent for replaces and updates. If you update an attribute in a document which belongs to a disk chunk which is being merged with another one, the update will be applied both to that chunk and to the resulting chunk after the merge. If you delete a document during a merge - it will be deleted in the original chunk and also the resulting merged chunk will either have the document marked deleted, or it will have no such document at all (if the deletion happened on early stage of the merging).

Freezing a table

FREEZE tbl1[, tbl2, ...]

FREEZE readies a real-time/plain table for a secure backup. Specifically, it:

  1. Deactivates table compaction. If the table is currently being compacted, FREEZE will wait for completion.
  2. Transfers the current RAM chunk to a disk chunk.
  3. Flushes attributes.
  4. Disables implicit operations that could modify the disk files.
  5. Shows the actual file list associated with the table.

The built-in tool manticore-backup uses FREEZE to ensure data consistency. You can do the same if you want to create your own backup solution or need to freeze tables for other reasons. Just follow these steps:

  1. FREEZE a table (or a few).
  2. Capture the output of the FREEZE command and back up the specified files.
  3. UNFREEZE the table(s) once finished.
  • Example
| file              | normalized                      |
| data/t/    | /work/anytest/data/t/    |
| data/t/t.0.spd    | /work/anytest/data/t/t.0.spd    |
| data/t/t.0.spds   | /work/anytest/data/t/t.0.spds   |
| data/t/t.0.spe    | /work/anytest/data/t/t.0.spe    |
| data/t/t.0.sph    | /work/anytest/data/t/t.0.sph    |
| data/t/t.0.sphi   | /work/anytest/data/t/t.0.sphi   |
| data/t/t.0.spi    | /work/anytest/data/t/t.0.spi    |
| data/t/t.0.spm    | /work/anytest/data/t/t.0.spm    |
| data/t/t.0.spp    | /work/anytest/data/t/t.0.spp    |
| data/t/t.0.spt    | /work/anytest/data/t/t.0.spt    |
| data/t/t.meta     | /work/anytest/data/t/t.meta     |
| data/t/t.ram      | /work/anytest/data/t/t.ram      |
| data/t/t.settings | /work/anytest/data/t/t.settings |
13 rows in set (0.01 sec)

The file column indicates the table's file paths within the data_dir of the running instance. The normalized column displays the absolute paths for the same files. To back up a table, simply copy the provided files without additional preparation.

When a table is frozen, you cannot execute UPDATE queries; they will fail with the error message "index is locked now, try again later."

Also, DELETE and REPLACE queries have some restrictions while the table is frozen:

  • If DELETE affects a document in the current RAM chunk - it is permitted.
  • If DELETE impacts a document in a disk chunk but was previously deleted - it is allowed.
  • If DELETE would alter an actual disk chunk - it will wait until the table is unfrozen.

Manually FLUSHing a RAM chunk of a frozen table will report 'success', but no real saving will occur.

DROP/TRUNCATE of a frozen table is allowed since these operations are not implicit. We assume that if you truncate or drop a table, you don't need it backed up; therefore, it should not have been frozen initially.

INSERTing into a frozen table is supported but limited: new data will be stored in RAM (as usual) until rt_mem_limit is reached; then, new insertions will wait until the table is unfrozen.

If you shut down the daemon with a frozen table, it will act as if it experienced a dirty shutdown (e.g., kill -9): newly inserted data will not be saved in the RAM-chunk on disk, and upon restart, it will be restored from a binary log (if any) or lost (if binary logging is disabled).

Unfreezing a table

UNFREEZE tbl1[, tbl2, ...]

UNFREEZE reactivates previously blocked operations and resumes the internal compaction service. All operations waiting for a table to unfreeze will also be unfrozen and complete normally.

  • Example



Flushes all in-memory attribute updates in all the active disk tables to disk. Returns a tag that identifies the result on-disk state (basically, a number of actual disk attribute saves performed since the server startup).

mysql> UPDATE testindex SET channel_id=1107025 WHERE id=1;
Query OK, 1 row affected (0.04 sec)

| tag  |
|    1 |
1 row in set (0.19 sec)