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PostgreSQL:

Adding an index to a table with big amount of data causes a lag for both SELECT and INSERT operations on that table, doesn't it?

While PostgreSQL does not support live (without lags) adding of indexes, how to solve the problem of adding an index to a table without lagging SELECT and INSERT (there is no UPDATEs on that table)?

My idea is to copy the table by small chunks to another table with the same structure, then in a transaction delete the original table and rename the new table to the original table name. How to ensure that the entire data is copied, while INSERT operations to the old table may happen?

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See Building Indexes Concurrently in PostgreSQL documentation.

CONCURRENTLY option of CREATE INDEX solves the problem in an easy way. Just add it to CREATE INDEX.

Be aware that while CONCURRENTLY option avoids lags, it does slow down building the index and that CREATE INDEX with CONCURRENTLY cannot be used in a transaction.

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