  Suppose a database containing $M$ records is replicated across $N$ servers,
and a user wants to privately retrieve one record by accessing the servers such
that identity of the retrieved record is secret against any up to $T$ servers.
A scheme designed for this purpose is called a $T$-private information
retrieval ($T$-PIR) scheme. Three indexes are concerned for PIR schemes:
(1)rate, indicating the amount of retrieved information per unit of downloaded
data. The highest achievable rate is characterized by the capacity; (2)
sub-packetization, reflexing the implementation complexity for linear schemes;
(3) field size. We consider linear schemes over a finite field. In this paper,
a general $T$-PIR scheme simultaneously attaining the optimality of almost all
of the three indexes is presented. Specifically, we design a linear
capacity-achieving $T$-PIR scheme with sub-packetization $\!dn^{M-1}\!$ over a
finite field $\mathbb{F}_q$, $q\geq N$. The sub-packetization $\!dn^{M-1}\!$,
where $\!d\!=\!{\rm gcd}(N,T)\!$ and $\!n\!=\!N/d$, has been proved to be
optimal in our previous work. The field size of all existing capacity-achieving
$T$-PIR schemes must be larger than $Nt^{M-2}$ where $t=T/d$, while our scheme
reduces the field size by an exponential factor.
