I am trying to make a tool that will live-copy a DB from one RethinkDB host to another, however I am hung-up on the fact I can't seem to find out what is actually in each index. I have tried
r.db('db').table('table').index_list()
and
r.db('db').table('table').info()
I even tried
r.db('db').table('table').index_list().info()
But all three only returned the names of the indexes and not what fields are in them. This makes it impossible to re-create the table on the destination DB exactly the same as the source.
What am I missing here? There has to be a way to do this, or is this just something missing from RethinkDB? If so, does anyone know why?
Indexes are computed from the documents in the table. If you read all of the documents from the first table (with e.g. r.table.run()) and insert them all into the second table, then re-create all the indexes, you will have successfully re-created the table.
As usual I only get answers from people who don't read my question or who want to answer questions that weren't asked.
The solution is to parse the data from
r.db('db').table('table').index_status()
Related
I use stored proceduers on DB instance "A" to store data in GTT. To get the original data i have to go over a DB-Link to DB instance "B". That for i put together the whole query and send it to remote DB instance.
This works fine. But sometimes it seems that Oracle is not using the best way or correct indexes for queries. Is there a way to force Oracle to use specific indexes? I tried to use hints, but honestly I dind't understand the difference between all these options.
Thanks for helping me!
There is a huge temptation to optimize a query one way when you want it to work another way. Adding hints is a temporary solution which can backfire on you when the amount or type of data in the table changes or when you upgrade to a newer version with a newer optimizer.
First, determine that there is a problem. Are all queries taking too long? Just some? Only the first one?
The easiest thing to do is to make sure the indexes on that table are up to date. Then look at optimizing the query by using the explain plan feature to see what indexes are being used.
It's also prudent to examine your data to see if the query is selecting different things or different amounts of records if it is time based.
I have a table in Hbase named 'xyz' . When I do an update operation on this table , it updates a table even though it is same record .
How can I control second record to not be added.
Eg:
create 'ns:xyz',{NAME=>'cf1',VERSIONS => 5}
put 'ns:xyz','1','cf1:name','NewYork'
put 'ns:xyz','1','cf1:name','NewYork'
Above put statements are giving 2 records with different timestamp if I check all versions. I am expecting that it should not add 2nd record because it have same value
HBase isn't going to look through the entire row and work out if it's the same as the data you're adding. That would be an expensive operation, and HBase prides itself on its fast insert speeds.
If you're really eager to do this (and I'd ask if you really want to do this), you should perform a GET first to see if the data is already present in the table.
You could also write a Coprocessor to do this every time you PUT data, but again the performance would be undesirable.
As mentioned by #Ben Watson, HBase is best known for it's performance in write since it doesn't need to check for the existence of a value as multiple versions will be maintained by default.
One hack what you can do is, you can use custom versioning. As show in the below screenshot, you have two versions already for a row key. Now if you are going to insert the same record with the same timestamp. HBase would be overwriting the same record with just the value.
NOTE: It is left to your application to get the same timestamp for a particular value.
Ok, tricky question I am trying to figure out where a database schema is storing a particular pointer. I know the pointer value I just don't what table it is in or what column. I know the pointer is 123123123. How do I check all table columns to see if any of them have that value?
Thanks.
In h2 you can use fulltext search, but then you would need to add all tables in the search scope and indexing.
If you need to index only primary keys, then it might be better but you still need to come up with individual FT_CREATE_INDEX() calls for each table. You can automate this with several languages or with ETLs (like scriptella).
If you've enough disk space, you could dump a SQL from your db and use a viewer for big files like glogg.
The advantage of the first solution is no external tools but you need to work out a specific indexing script for SQL for any existing or new table. The 2nd solution is a 1 time fix.
I use SQL Search from RedGate. It's free and it helps you find any text anywhere in the database.
https://www.red-gate.com/products/?gclid=CjwKEAjwiYG9BRCkgK-G45S323oSJABnykKAE7IH_EMhnmq7OdLdXljfIkdGZrDD6OnOrT4VB0agahoCVn3w_wcB
I have configured free text search on a table in my postgres database. Pretty simple stuff, with firstname, lastname and email. This works well and is fast.
I do however sometimes experience looong delays when inserting a new entry into the table, where the insert keeps running for minutes and also generates huge WAL files. (We use the WAL files for replication).
Is there anything I need to be aware of with my free text index? Like Postgres maybe randomly restructuring it for performance reasons? My index is currently around 400 MB big.
Thanks in advance!
Christian
Given the size of the WAL files, I suspect you are right that it is an index update/rebalancing that is causing the issue. However I have to wonder what else is going on.
I would recommend against storing tsvectors in separate columns. A better way is to run an index on to_tsvector()'s output. You can have multiple indexes for multiple languages if you need. So instead of a trigger that takes, say, a field called description and stores the tsvector in desc_tsvector, I would recommend just doing:
CREATE INDEX mytable_description_tsvector_idx ON mytable(to_tsvector(description));
Now, if you need a consistent search interface across a whole table, there are more elegant ways of doing this using "table methods."
In general the functional index approach has fewer issues associated with it than anything else.
Now a second thing you should be aware of are partial indexes. If you need to, you can index only records of interest. For example, if most of my queries only check the last year, I can:
CREATE INDEX mytable_description_tsvector_idx ON mytable(to_tsvector(description))
WHERE created_at > now() - '1 year'::interval;
Is there any way to force oracle to use index except Hints?
No. And if the optimizer doesn't use the index, it usually has a good reason for it. Index usage, if the index is poor, can actually slow your queries down.
Oracle doesn't use an index when it thinks the index is
disabled
invalid (for example, after a huge data load and the statistics about the index haven't been updated)
won't help (for example, when there are only two different values in 5 million rows)
So the first thing to check is that the index is enabled, then run the correct GATHER command on your index/table/schema. When that doesn't help, Oracle thinks that loading your index will actually take more time than loading the actual row values. In this case, add more columns to the index to make it appear more "diverse".
You might take a look at oracle stored outlines. You can take an existing query and create a stored outline and tweak the query just like hints. It is just very hard to use. Do some research before you decide to implement stored outlines.
You can add hints into the query that will cause it to look more favorably on one index over another index.
In general if you have collected good statistics on all the tables and indexes Oracle usually implements very good execution plans.
If your query doesn't include the indexed field in its conditions, then the DB would be foolish to use the index. Thus, I second Donnie's answer.
Yes, technically, you can force Oracle to use an index (without hints), in one scenario: if the table is an index-organized table, then logically the only way to query the table is via its index because there is no table to query.