indexer program configuration options


Lemmatizer cache size. Optional, default is 256K.

Our lemmatizer implementation (see morphology for a discussion of what lemmatizers are) uses a compressed dictionary format that enables a space/speed tradeoff. It can either perform lemmatization off the compressed data, using more CPU but less RAM, or it can decompress and precache the dictionary either partially or fully, thus using less CPU but more RAM. And the lemmatizer_cache directive lets you control how much RAM exactly can be spent for that uncompressed dictionary cache.

Currently, the only available dictionaries are ru.pak, en.pak, and de.pak. These are the russian, english and german dictionaries. The compressed dictionary is approximately 2 to 10 MB in size. Note that the dictionary stays in memory at all times, too. The default cache size is 256 KB. The accepted cache sizes are 0 to 2047 MB. It’s safe to raise the cache size too high; the lemmatizer will only use the needed memory. For instance, the entire Russian dictionary decompresses to approximately 110 MB; and thus setting lemmatizer_cache anywhere higher than that will not affect the memory use: even when 1024 MB is allowed for the cache, if only 110 MB is needed, it will only use those 110 MB.

On our benchmarks, the total indexing time with different cache sizes was as follows:

  • 9.07 sec, morphology = lemmatize_ru, lemmatizer_cache = 0
  • 8.60 sec, morphology = lemmatize_ru, lemmatizer_cache = 256K
  • 8.33 sec, morphology = lemmatize_ru, lemmatizer_cache = 8M
  • 7.95 sec, morphology = lemmatize_ru, lemmatizer_cache = 128M
  • 6.85 sec, morphology = stem_ru (baseline)

Your mileage may vary, but a simple rule of thumb would be to either go with the small default 256 KB cache when pressed for memory, or spend 128 MB extra RAM and cache the entire dictionary for maximum indexing performance.


lemmatizer_cache = 256M # cache it all


Maximum file field adaptive buffer size, bytes. Optional, default is 8 MB, minimum is 1 MB.

File field buffer is used to load files referred to from sql_file_field columns. This buffer is adaptive, starting at 1 MB at first allocation, and growing in 2x steps until either file contents can be loaded, or maximum buffer size, specified by max_file_field_buffer directive, is reached.

Thus, if there are no file fields are specified, no buffer is allocated at all. If all files loaded during indexing are under (for example) 2 MB in size, but max_file_field_buffer value is 128 MB, peak buffer usage would still be only 2 MB. However, files over 128 MB would be entirely skipped.


max_file_field_buffer = 128M


Maximum I/O operations per second, for I/O throttling. Optional, default is 0 (unlimited).

I/O throttling related option. It limits maximum count of I/O operations (reads or writes) per any given second. A value of 0 means that no limit is imposed.

indexer can cause bursts of intensive disk I/O during indexing, and it might desired to limit its disk activity (and keep something for other programs running on the same machine, such as searchd). I/O throttling helps to do that. It works by enforcing a minimum guaranteed delay between subsequent disk I/O operations performed by indexer. Modern SATA HDDs are able to perform up to 70-100+ I/O operations per second (that’s mostly limited by disk heads seek time). Limiting indexing I/O to a fraction of that can help reduce search performance degradation caused by indexing.


max_iops = 40


Maximum allowed I/O operation size, in bytes, for I/O throttling. Optional, default is 0 (unlimited).

I/O throttling related option. It limits maximum file I/O operation (read or write) size for all operations performed by indexer. A value of 0 means that no limit is imposed. Reads or writes that are bigger than the limit will be split in several smaller operations, and counted as several operation by max_iops setting. At the time of this writing, all I/O calls should be under 256 KB (default internal buffer size) anyway, so max_iosize values higher than 256 KB must not affect anything.


max_iosize = 1048576


Maximum allowed field size for XMLpipe2 source type, bytes. Optional, default is 2 MB.


max_xmlpipe2_field = 8M


Indexing RAM usage limit. Optional, default is 128M.

Enforced memory usage limit that the indexer will not go above. Can be specified in bytes, or kilobytes (using K postfix), or megabytes (using M postfix); see the example. This limit will be automatically raised if set to extremely low value causing I/O buffers to be less than 8 KB; the exact lower bound for that depends on the indexed data size. If the buffers are less than 256 KB, a warning will be produced.

Maximum possible limit is 2047M. Too low values can hurt indexing speed, but 256M to 1024M should be enough for most if not all datasets. Setting this value too high can cause SQL server timeouts. During the document collection phase, there will be periods when the memory buffer is partially sorted and no communication with the database is performed; and the database server can timeout. You can resolve that either by raising timeouts on SQL server side or by lowering mem_limit.


mem_limit = 256M
# mem_limit = 262144K # same, but in KB
# mem_limit = 268435456 # same, but in bytes


How to handle IO errors in file fields. Optional, default is ignore_field.

When there is a problem indexing a file referenced by a file field (sql_file_field), indexer can either index the document, assuming empty content in this particular field, or skip the document, or fail indexing entirely. on_file_field_error directive controls that behavior. The values it takes are:

  • ignore_field, index the current document without field;
  • skip_document, skip the current document but continue indexing;
  • fail_index, fail indexing with an error message.

The problems that can arise are: open error, size error (file too big), and data read error. Warning messages on any problem will be given at all times, irregardless of the phase and the on_file_field_error setting.

Note that with on_file_field_error = skip_document documents will only be ignored if problems are detected during an early check phase, and not during the actual file parsing phase. indexer will open every referenced file and check its size before doing any work, and then open it again when doing actual parsing work. So in case a file goes away between these two open attempts, the document will still be indexed.


on_file_field_error = skip_document


Write buffer size, bytes. Optional, default is 1 MB.

Write buffers are used to write both temporary and final index files when indexing. Larger buffers reduce the number of required disk writes. Memory for the buffers is allocated in addition to mem_limit. Note that several (currently up to 4) buffers for different files will be allocated, proportionally increasing the RAM usage.


write_buffer = 4M